Ac'97 will fit into the hd audio port, but it won't do anything. Of course you don't have to plug it in if you don't use the front ports. My one friend has never used them, and I didn't for a while either.
Thank you for sharing your experience. I just left it un-plugged. There is an S/PDIF audio outlet in the back panel, so i may not use the front outlets anyway.
I also noticed that for all the builds I have done in the past the front panels are mostly just above the middle of the case, so the distance between the front outlets and the ports on the motherboard is not that far away. This is the only one I have done so far whose front panel is right at the top of the case.