Hi there ~
I understand your concerns. Unnoticeable bump on lip after being scratched by a homely dog does not seem to be of concern. It depends on weather you dog was vaccinated for all the viral and other illnesses. I also think that you should visit with a doctor and consult the veterinarian that takes care of your dog, so as to allay your anxiety
about the issue.
I hope this helps. Take care and have a lovely day!