Is it safe to skip a dtap shot if my baby had a bad reaction in the past?

Generally NO. It depends upon what the reaction was. Fussiness, fever, or soreness are aggravating, but not overly dangerous. An anaphylactic (severe allergic) or severe neurological reaction may be the only reasons not to immunize again. Discuss with your doctor.
No. Though it's not very common, infants can have fevers after their vaccination. Vaccinations work by stimulating the immune system and it's the immune response that can occasionally cause a fever. There are very few reasons, other than significant allergic reactions, to delay the next dose in a series. This is from the cdc: http://www.Cdc.Gov/vaccines/recs/vac-admin/contraindications-vacc.Htm.
It depends.. In most cases, previous reactions to a vaccine are not a reason to avoid future doses. It is important for your child to be fully immunized against life threatening disease like diptheria, pertussis and tetanus. Tell your baby's doctor as much as possible about the previous reaction so that you can make an informed decision together.