I am substituting crab with shitake mushrooms. The recipe calls for mint...will that combination taste bad?

I would substitute. Maybe basil.

Crab and shitake mushrooms have very different flavor profiles, and I agree that mint sounds off here. I might just go with chives or something else in the onion family.

I would pull out the mint - and - lemon, and sub in lime.

I would sub mint with chives and sub red wine vinegar or balsamic for the lemon. There is nothing crab-like about shitake mushrooms and you really need earthier flavours than mint and lemon.

I am not sure from your question whether you are using crab or shitake in your recipe. Crab combined with mint doesn''t do much for me, but in Italy, mint is used with chantarelles, so I might be tempted to give it a try with shitake.