my question is: I am grilling a stuffed whole salmon - stuffed with crab, shrimp, dill, scallions, garlic, shallots - what to add to not be bland

I'd use something acidic, salt, pepper and maybe a little heat. And also lose about half of the stuffing ingredients. Way too much going on for my taste. Just the scallions and crab would be enough to let a grilled salmon shine.

and some butter.

As long as you add seasonings (which you say you have) and remember the salt and pepper, I don't see why what you've described would be bland. I might add some acidity (lemon) to give it some balance.