Yes it would, the main difference being that it doesn't support Firewire natively, whereas win98se does (in fact WDM support was hugely improved in the update). Whether this means that it won't work at all is debateable. I think that it would, due to the fact that it will work on ME, but you won't be able to use Firewire. A quick search using Google might give you a more definite answer.
ATI don't "support" it mainly because Win98 is 4 years old and effectively obsolete. Not even Microsoft officially "support" it anymore.