Really, the answer should be "No". I don't have any of my books at work, but here's the whys.
Best explanation for summon spells is that they essentially call an astral projection of an average member of the race in question. I've also heard dream projection. Summon Monster is limited to extraplanar creatures only. Summon nature's ally to animals. And if you have FR, Summon Undead to, well, undead. Even with the variant rules for summoning individuals, they are an average member of their race or species (as I recall).
1) - PCs are not average members of their species. Best case scenario of summoning party members would be a likeness of the character but with all his attributes set to 10 or 11 (or appropriate), with average feats for his class, and average equipment for a member of his species. And then you'd need a summon spell level that would be able to summon a creature of the PCs CR/HD. That get's high-level fast. But frankly, I wouldn't even allow that.
2) - PCs are rarely extraplanar creatures, and are definitely not just Animals (referring to Type), though I've seen Undead PCs. In any regard, summoning, regardless of spell, seems to bring ideal generics from another plane of existence. Reading the summoning sub-school description suggests this with the statement about reforming after being unsummoned. While it does not explicitly state it, that is a common trope of demons, devils and otherworldly creatures. Furthermore, even if it did "work", summoning says it takes 24 HOURS for the summoned creature to reform if reduced to 0 hp. If you get whacked, there is NO recourse, since there isn't even a body for the healer at your safehold to patch up and heal.
3) - Given the similarities described between not being dead but reforming, and instant summoning to a locale And the description of passing planar gates/portals while in Astral form, if I would even consider it - it would be up there as a 9th level spell. And watch out for githyanki.
4) - There are precedents for Calling spells however. In FR, the mage Darsson made a spell which invokes part of his truename. He gave this spell to friends, so that they could instantly call him to their side - suck to be in the bath, and suddenly find yourself in a major land war. 3rd edition compromised with the Refuge spell (if I recall correctly). In all instances and precedents, the target is called, actually physicially brought to the location.
So, even if your characters are naturally extraplanar, they are likely on the same plane as the summoner. I'd say no go. If you are on a different plane and suddenly count as extraplanar, you aren't average for your race. No go, again. Sounds like an astral or dream projection to me. Maybe - if you are willing to cast a single 8th or 9th level spell PER PC summoned. Now, if the sorcerer has great scout spells, evades the traps, and has a CALLING spell to bring each of you, one at a time, to his location. That I might go for.
And lastly, and most importantly. Summoned people hang out for rounds. The summoned characters won't be there, can't make a meaningful contribution or be involved in the adventure - hope you trust you sorcerer implicitly when it comes to loot sharing and information exchange. As players, you are uninvolved and cut out of the game while the DM plays a one on one session with the sorcerer's player until he needs your fat butts to stand between him and the nasties, or disarm a trap (if you are around long enough). Hope you like doing something else until the bat signal flashes.
And that's probably why I, as a DM, would never allow that.