Technically... yes.

Practically... Sheer impossible to combine 2 Voodoo Cards without severe Driver interference.

Also, the TV out on the Secondary might be impossible to address due to Driver limitations (development was on Gaming and OpenGL/DirectX compatibility of a single card, not on secondary device features).

Fixing the first Problem would require massive manual editing of at least one Driver (Primary) and working out a functional sequence of installation is needed.
Very tough job, its easier to use a non-3dfx Card as secondary with guaranteed functionality e.g. for modern and hassle-free TV out.

It's posible, i have a running setup with a Voodoo 4 PCI and a Voodoo 3 3000 AGP. There are no problems in desktop mode under Win2k, i use the V4 as primary device for my monitor and the V3 as secondary for my TV. But there might be some problems in 3D mode, some games works properly on both devices (e.g. UT and NFS3), but some games or applications (e.g. 3Dmark2001) have problems on the card installed first.