nouveau question

I found a cheap SCSI drive and got my other PWS500a (el segundo) to 
work.  I put my nVidia card in and made a kernel with a built-in nouveau 
driver.  The nouveau framebuffer console works fine.
Gentoo refuses to acknowledge VIDEO_CARDS="nouveau" on my alpha.  I see 
how USE flags can be masked in profiles, but I don't know how video 
cards are masked.  I'm sure someone could tell me quicker than I can 
figure it out myself.

Is nouveau being prevented because alpha can't run it?
Am I missing some obvious answer?

Adios, DW