Is it harmful to ingest a scab from a healing basal cell surgery site?

It is not recommended that you injest scabs. The wound should be allowed to heal naturally, and if accidental ingestion does occur, it would pass through the digestive system and out of your body the next time you relieve yourself.

This is a unique question but you can rest assured that ingesting the scab will not risk your health in terms of cancer spread. That being said, I don't recommend ingesting a scab. And as already stated a scab should not be there...all dried blood and debris should be gently removed daily as keeping the wound clean will promote better scar formation.

This is a bit of an odd question. However, the purpose of Mohs or surgical procedures is to leave the area without any further cancer there. Thus, there should not be any cancer left behind. However, it's advisable not to let surgical sites scab because this leads to worse scarring and divets. "This answer has been solicited without seeing this patient and cannot
be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."