Is Microsoft Intellimouse or other scrolling mice supported?

Partly (with native XSun). Configure it as a 3-button PS/2 mouse.
The wheel won't scroll anything, but pressing the wheel down
is the same as pressing the middle button.
The same holds true for Logitech's MouseMan Wheel mice.

Update:
I understand the new version 1.2 of Intellimouse does not work
with Solaris's XSun.
However, XFree86 and Xi Graphics X Windows graphics card server software
do support wheel mice [Thanks to Alan Orndorff].