We *can* EQ, we *do* EQ -- Ideally, we're not "fixing" things (although it happens. A lot. A really, really lots).
Ideally, we're EQ'ing to (1) aid in translation across systems and (B) add cohesion to the project holistically.
But no doubt - If the client can hear that it's muddy and they have the capability to fix it in the mixing stage, there's absolutely no reason not to do so.