Well, I've just spent a couple of hours going through the
RPG Geek database looking to see who these people were and if they contributed to Different Worlds. The results are below, along with a bunch of links if you want to investigate further.
As an aside, the RPG Geek database is quickly becoming very impressive. They recently added a feature allowing the addition of individual article credits, and some of that was very helpful in this research, although I don't think the early DW issues are all broken out individually yet.
Steve Perrin - original designer of RuneQuest and other BRP systems. Also co-wrote CM9 Legacy of Blood, a D&D Companion level adventure, and FRC2 Curse of the Azure Bonds, the adventure conversion of the D&D computer game/novel from TSR. Contributed to many issues of DW, including #2, #3 and #7.
Gary Gygax - a non-entity sent a letter by mistake. Not to be confused with E.Gary Gygax, co-progenitor of our entire hobby.

Didn't contribute to DW, as far as I can tell.
Ken St Andre - creator of Tunnels and Trolls and co-designer of Stormbringer. Ended up contributing several articles to Different Worlds, including #1 and #7.
David Hargrave - creator of the Arduin Grimoire, an alternative take on D&D. Contributed to at least 3 issues of DW (1, 2 & 31).
Marc Miller - creator of Traveller. Contributed to DW #1 and #9.
Tim Kask - editor on early D&D products, (and had to rewrite/create a lot of Supplement 2, Blackmoor). Later created his own magazine (Adventure Gaming, IIRC). Don't think he contributed to DW.
Ed Simbalist - Co-designer of Chivalry & Sorcery and Space Opera (recently discussed on Grognardia). Contributed to DW #1. (Sadly died in 2005).
Jim Ward - Creator of Metamorphosis Alpha and Gamma World, as well as contributing to a lot of early D&D. Contributed to DW #5 and #7.
M.A.R. Barker - Professor. Created Tekumel (which inspired Feist's Kelewan). Eventually contributed to DW #47.
David Feldt - Creator of
Legacy in 1978 - and if you haven't heard of it, don't worry, about no-one has. Contributed to DW #2.
Wilf Backhaus - Co-designer of Chivalry & Sorcery. Died in 2009. Did not contribute to DW, as far as I can see.
Mark Swanson - Editor of the Wild Hunt (an early zine/publisher as far as I can see). Contributed to DW #1.
Paul Jaquays - Illustrator for many companies, also did a lot of design work, including DQ1 The Shattered Statue for AD&D. Contributed to DW #1 and DW #24.
Steve Marsh - There are two Steve Marsh's; so I'm guessing it's the editor of the D&D Expert Set and creator of the Sahuagin. The fact that he contributed to DW #1, #3 and #13 makes this more likely.
John M Snyder - I have absolutely no idea.
Eric Goldberg - Co-designer of Paranoia and DragonQuest who later ran West End Games for a while. Contributed to DW #2.
Scott Bizar - Founder of FGU and co-creator of Chivalry & Sorcery. Contributed to DW #5.
Dave Arneson - Co-creator of D&D. Contributed to DW #3, #8 and several in the 40s.
Nikolai Shapiro - Early Runequest gamer at SoCal (according to this
rpg.net reference), but I can find no design or article credits to his name.
Lee & Barry Gold - Lee contributed to DW #1, #6 and #8, and worked for FGU, ICE and Steve Jackson Games. I can't find any credits for Barry Gold.
Ian Livingstone - Co-founder of Games Workshop and co-creator of the Fighting Fantasy Gamebooks. Involved in the original distribution of D&D into the UK. Did not contribute to DW, as far as I can see - but was very involved with White Dwarf.
Paul Hume & George Nyhen - Paul Hume was the co-designer of Bushido and Aftermath (FGU) and Shadowrun (FASA). Didn't contribute to DW. George Nyhen was the co-designer of Tyr Gamemaker's "
Space Quest". Also didn't contribute to DW.
Greg Costikyan - A long list of credits, including Paranoia and Star Wars, and one of my favourite light RPGs, Teenagers from Outer Space. Contributed to four issues of DW, including #1 and #11.
Darryl Hany & Frank Chadwick - Darryl Hany contributed to a few early Traveller products and co-designed "En Garde!" , but didn't write for DW. Frank Chadwick co-founded GDW Games and has a lot of wargames to his credit along with a few RPG products (including early Traveller and En Garde!). He wrote an article for DW #9 (an introduction to the Imperium in Traveller, alongside Marc Miller!)
B Dennis Sustare - Lent his name to
Chariot of Sustarre, a high-level druidic spell in D&D. Originator of the druid class in D&D. Co-designed Bunnies and Burrows. Contributed to DW #1, #3 and #19.
Michael J Scott - assumed name of Michael Scott Kurtick, co-designer of Space Patrol. No contributions to DW, as far as I can see.
Leonard Kanterman - Designer of Starships & Spacemen (1978) and Star Explorer. Contributed to DW #1, #2, #6, #8 and #13. (A post from him on RPGGeek discussing the games is
here.)
Nicholas Smith - likely to be the author of the
Complete Warlock (1978), an unofficial supplement/variant to/of original D&D. I can't see any contributions to DW.
Steve Jackson - Ah, but which one? I'm not sure. One of them contributed to DW #2 (in an article co-written by David Feldt - "My Life and Roleplaying"). At present, the RPG Geek database has it down as the US Steve Jackson, but without someone looking at the actual issue, it's a bit hard to tell.
Steve Lortz - Interviewed in DW #1, also appearing in #2, #3, #4, #5 and #9. Mainly a miniature sculptor fascinated by ducks, according to his rpggeek entry. Co-designed Star Rovers.
Cheers!