You can't use the dats in romcenter.
You need to use clrmamepro.
The only way of creating dats for whdload games is by either:
A) Scanning the contents of subfolders inside the zips. This is problematic with non-windows filenames and causes a lot of headaches. Plus, romcenter can't scan the contents of subfolders inside the zips.
B) Treat each zip file as a solid file. This works fine in clrmamepro, but unfortunately isn't supported by romcenter.
So, you'll need to use clrmamepro, or not use the dats!