Well it doesn't require it.
I've got an Athlon XP 1800, GF4 4200, in AGP mode, with the agpgart module doing the AGP work, and I haven't seen lockups when running any OpenGL or other graphics-oriented threads. This includes a couple of hours of playing UT2k3 at a time, a whole bunch of zsnes goodness, and a lot of Descent 3. Even X, which under 2.4.18 had intermitent issues with lockups, is fine.
I'm running 2.4.19, perhaps AMD's patch was incorporated into it? If that was the case, then either form of AGP handling should work fine...