I think that maybe mickey could have been a TESTER for the drive forms, not the originator or inventor. The drive forms have probably been an old battle style used by plenty keyblade masters. However when their numbers decreased, the ability to drive slowly disappeared. Then Mickey came along to try to learn it.
Ven is proably his own person tied to Roxas somehow. Maybe, due to the battle with Master Xehnaort, he needed to recover. So he, somhow fused with Sora, giving Sora the power to weild the keyblade. Then, when Sora became a heartless, Ven was realesed, however he forgot everything. That is why Xemnas gives Roxas a new name, as see in KH2:FM+. Well... this is what I think
