Welcome to the world of Rotties! No it's not a problem, you're likely going to need the occasional spit rag strategically placed around the house to wipe this off for him. They usually don't drop away, they just hang until his mouth hits something- like your pants, the wall, the couch- you get the idea.
Good luck with this big guy.
Dog Veterinarian
DVM, Emergency Veterinarian; BS (Physiology) Michigan State Univ