Yeah, let's keep it to a check. DC 20?
Oh all right, if we're bothering with by petty concerns like consistency.
DC20 is too high going by the SRD examples:
9HD, CR7 Flesh Golem - Leatherworking DC 13.
11HD, CR10 Clay Golem - Pottery & Sculpting DC 15.
14HD, CR11 Stone Golem - Sculpting & Stonemasonry DC 17.
18HD, CR13 Iron Golem - Armoursmithing & Weaponsmithing DC 20.
So, that looks like the Craft DC is CR plus 5-7 or half Hit Dice plus 9-11.
That suggests a DC around 10-12 for the Craft (alchemy) check.
I'd also consider a Craft (leatherworking) check, since a lot of cutting & stitching seems to be involved in a Grayman's creation, like with a Flesh Golem.
As far as controlability, let's say it's unknown how to control them for more than a short period of time. That would allow Lyzandred to have been tricked. What I really want to know is how he got killed by a bunch of 3HD monsters, though. He must have been pretty high level.
I suspect he just thought he was safe so had a lot of research spells in his repertoire that day, and they got into melee before he react. (Poor surprise check, no doubt).
I'd also note that there is no mention of there being a wizard's corpse in the laboratory with the greymen. I can see only one likely explanation.
They ate him to feed their oozes.