They should be fine.
The reason the internal is not an issue is because butts are 'intact' cuts, i.e., not ground or injected, and the likelihood of internal bacteria is vanishingly small. Surface bacteria are the issue. Likely bacteria present on butts in packaging might have enough time to grow at higher surface temps but these bacteria will be reduced sufficiently or eliminated during cooking. (Time @ temp is the issue and one looks at both variables to determine possible problems but I'm not concerned based on what you've said.)
Bacteria that might have been introduced to the surface, e.g., if you had removed the butts from packaging and, perhaps, applied rub, would be the next concern and then one would look at those variables to determine potential problems.