Looking at the discs, the EtherLink III driver appears to have already moved to WDM (elnk3.sys instead of .vxd) even in "first edition" Windows 98.

The Cirrus Logic 542x drivers stayed as VXD, however, there is no guarantee they would still be compatible with Win95. I guess you could try overwriting cirrus.vxd, cirrus.dll, and cirrus.drv with the Windows 98 versions if you wanted to see. I didn't see any BSWAP or XADD insructions in them in a quick check via objdump.

I vaguely recall claims that installing DirectX would update video drivers, but looking at the DX5 package on the OSR2.5 CD, I don't see any drivers. Anyone know the backstory there?

Note that both the Cirrus 542x and 3Com EtherLink III predate Windows 95, and were both ubiquitous both during Windows 95 development, and during the window (pun) of development between the original release and OSR2.5. If there were any fixes they needed, they would've made it into OSR2.5. By then, both of these were old in the tooth, and I can't imagine the priority for 98 was anything other than don't break them.

Thanks.
Regarding DX5: the latest driver for Cirrus GD are in the DX6.1 package.