It will depend on what the Dell disk was like. If you have been able to install HyperOS then it sounds like you have a full Win98 disk.
Only problem may be a lack of drivers. I recently tried to use a Dell XP Pro disk on a non-dell PC and it wouldn't install because the graphics card drivers weren't present.
Win98 doesn't have any of the problems of WPA so as long as you have the correct drivers you should be ok.
It is normamly advisable to do a clean install when you add a new mobo to a PC because of the problems that can exist with drivers, though you can get away with not doing it. Just expect to see lots of "new hardware found" messages when you first use the new mobo with old hard drive.