That will work fine if your mobo doesn't have agp issues you can't work around.
Most games give a choice of what card to use, or if they don't they will default to the Geforce most of the time, as its the primary display device.
A common setup really.

The Voodoo2 being a secondary video device, will show up appropriately as a second non-primary display device for Direct3D giving priority to the Geforce, and to use in OpenGL you'd have to use a MiniGL or a separate OpenGL ICD to explicitly use the Voodoo (though some games are stupid to default to it, like RTCW). It'll hardly cause conflict issues (unlike Geforce and the PowerVR PCX-2)

Plus you can disable Voodoo2 d3d support in the Voodoo2 control panel or through regedit.

^^ As above, such a setup works very well 😀

Well, I can say that the Voodoo 2 SLI + GeForce FX5200 AGP setup flatout don't work correctly with the ASUS P5A v1.04 [ALi (Aladdin) chipset]. It's extremely spotty usually not working at all. So I tried it on the ASUS P3B-F v1.04 Pentium III setup and it works great! Go fig. heh... looks like i'll be using the ASUS P5A AMD K6-3+ system for "DOS Time Machine" useage only afterall.

Actually Deus Ex runs significantly faster on the Pentium III too, it was literally crawling on the AMD system even in Glide mode and plenty of system RAM. Now i'm starting to see why people chose Intel back then for 3D gaming over AMD K6-2 or AMD K6-3... the AGP support is crap [fault of the chipset creators and not AMD's fault]. I guess the FPU is weaker in the AMD K6-2 and K6-3 chips too though, but I never realized it was THAT big of a difference [as I witnessed with Deus Ex].

Deus Ex was a dog on every computer in its day, one of the early demanding games prior to Giants in the same year. Not even a Geforce2 will help it.