1. IN vaccines tend to have a quicker mucosal response - so the calf may produce antibodies in 2-3 days vs the typical 14 that most injectable vaccines require. In HR calves that are or will be exposed to pathogens soon, early protection would be of benefit followed by the later immune response by the injectable. Possible to have a better immune response through use of two vaccines by different routes also; I don't recall the latest literature.
2. BS and Inforce are both modified live viral vaccines. If they were modified live bacterial vaccines then maybe an antibiotic could be a potential issue. Antibiotics have absolutely no effect on viruses so it would not interfere with the vaccine response.
Apologies, didn't see your post - been a little hectic on this end and I'm only just going through posts and PMs.