I havent read throught the entire thread
I did shared care with my GP/team midwifery for my first baby. My GP practised obstetrics so I dont know whether that makes any difference, but I never saw anyone other than him and midwives until I was overdue and he was on leave.

They could be using a 36 weeks appt it to offer you the GBS test and an ultrasound, but you are not obliged to have either of them - regardless of what they tell you all tests are voluntary.
Some OBs routinely offer GBS swabs while others do not, and a 36 week scan is certianly not 'routine' at least not in the public system here (Vic) its normally requested if there are other "complications".

FWIW, I am not having GBS swab at 36 weeks. I have agreed to ABs if I go into labour before 37 weeks, otherwise I may decide to have the GBS swab a lot closer to my EDD, maybe 39 or 40 weeks, given that DS was 11 days over and I was negative last time. (as an aside i find it odd that if you were postitive last time, you are assumed positive every time, but its not the same with a negative result...)

They may also just want to inform you as to what to take with you to the hospital, visiting times (partners and grandparents for example may have different visiting hours to whats advertised to the public) that sort of thing.