I think we talked about this the other day and I said that I myself am a construction worker and server. My girlfriend is a server as well and has a two year old daughter and we still don't have a problem making rent. We are currently renting ( closing on my first property next week) and have never missed a payment and haven't given landlord any grief. I guess what I am trying to say is just because they have jobs that most of the time are looked down upon from a financial standpoint, doesn't mean they would be bad tenants.
If dad is willing to cosign and their income meets your criteria, along with everything else like criminal background, good credit and everything I don't see why not. Even if they are to break up, dad is on the lease and probably won't want his credit ruined, so he wont miss the payment or he will make her find a roommate to make they payment. If she is in school and working that right there says she has some responsibility.
The property I am buying is about a block away from a university so I am attracting mostly college students. Therefore I am basically having to count on cosigners for my tenants.