I spent almost a year feeding fresh little neck clams every day or every other day in an effort to acclimate a CBB. I never had an issue as far as I could tell. (just don't leave uneaten clam to rot - obviously)
Yup. When I get new regal angelfish, live clams, mussels, and oysters, are constantly being offered. I shuck the shellfish and rinse if a little and in it goes. No issue. I also feed the tank cut up clams often.
I just scrub the shell a bit. Most of the shellfish we get from grocery store are super clean. After all, it is food grade. Sometime, the mussels might come with some tough stringy algae on the shell. The tangs love to peck at that stuff too.