x11-drivers/xf86-video-vesa is keyworded ~ or stable for several non-x86 architectures. Except x86_64 (and ia64?) I don't see how VESA could possibly work for archs not based on x86. The video_cards_vesa USE flag is masked in some ppc64 and all sparc profiles, so somebody realised the driver wouldn't work. (For the record: it compiles nicely on sparc64, but, as expected, doesn't do anything.) I think the arch keywords and the masking of video_cards_vesa need to be checked.
*** Bug 145305 has been marked as a duplicate of this bug. ***
The X server has a cute little built-in emulator called x86emu.
Fixed in CVS, thanks.