My school has a pre-health advisory committee. Really, anybody who wants to get a letter can. Last year, I went for the committee letter ... all of my individual LORs were in by July or August (or earlier, I can't remember, point is that it was EARLY) ... my school committee rolled out my letter to AADSAS in November. By the time it reached the schools in December, I had already been rejected at two schools.
So naturally, this cycle I opted to go with individual letters even though a committee letter was available. I haven't run into any problems with this. Through AADSAS, I had: 2 bio profs, orgo chem prof, dentist. Additionally another dentist sent letters to all of the schools on her own (not through AADSAS). I didn't submit a 'non science' letter even though some schools ask for non-science prof. I think Creighton specifies one non-science prof, but I withdrew from there so don't know if I really needed it. Other schools I applied to just specify things like "x-number science prof, 1 other prof" .. schools that I applied to which ask for one 'other prof' letter include NJDS and NYU, both of which I received interviews at despite not having a non-science letter.
WVU also required a physics letter, so I did have a LOR sent there from my school's physics department head. I didn't have this sent to any other schools.
I haven't gotten an interview from UDM and am going to be withdrawing from there anyway, but nowhere among the bajillion letters they have sent me have they mentioned there being a problem with the LORs they've received from me. Also haven't heard anything from BU regarding any problems with my application, but I will be withdrawing from there as well.
This is my experience, hope the info helps. Your results may vary.