I didn't respond because I couldn't give a "definite answer".
There are no definite answers with vgas.

Oh alright I'll try.

A good range of Nvidia cards right up to Geforce 4s may work,
or can be made to work by altering vgadb, or tweaking code.

You will need to check the archives, as there are several
semi-independent efforts at improving support.

The fundamental problems are

1. acceleration may or may not work
2. depths > 8 may not work
3. snow may appear on the screen
4. laptop screens using Geforce Gos won't work

This is all down to a partial but incomplete port of the Xfree86 4
driver. It is believed that a complete port will make the vast majority
of cards work. In particular, there is some "memory access
optimisation" code in there which is missing from the Plan 9 version,
and could easily account for most of these problems (except 4).

As I say, check the archives. There has been a lot of traffic on the
subject.

As a summary, you have a good chance of getting most cards to work
acceptably in 8 bit depth, except laptops.

There you are; definitive, if not really definite.

Nigel