Is there a way to dissolve a cut between two clips in fcpx.....?

Yes. Why would you need to make them a compound clip? Or to you mean you're trying to put a transition between two connected clips and it makes them into a secondary storyline? No. There is no way to not do this. You can only have transitions in a storyline.

Go to the transitions menu and the first option should be Cross Dissolve. Just drag that to the cut you want it and boom.

I think you've got the "compound clip" part wrong. You need to make 2 clips part of a storyline (or a compound clip) to dissolve between them.

Maybe you're using a compound clip (Opt-G) when you could just be using a storyline (Cmd-G)?

But think about this. It doesn't make sense to put a dissolve between 2 clips without forcing them to be linked (in the way that a storyline does). The same way you put a (explicit) dissolve between clips on different tracks, in other video editors. It doesn't even make sense.