I just had my first baby (at home). When I asked at my first homebirth midwife appointment, she referred me to an OB who has seen some of the women she served in the past. I wanted to have the testing done to make sure I was truly low risk and that the homebirth would be "safe." When I first went to see the OB, his policy was that he would treat me like any other patient, he expected that I would go to all appointments and then "oops she just didn't show up at the hospital." I was fine with doing that because he seemed very supportive of natural childbirth and if I ended up needing to choose hospital birth, I would already have an established relationship.
However, about halfway through my pregnancy, he got a lot of pressure from the OBs who back him up--he is in practice by himself so it he can't make it, they were refusing to cover him. (The other major practices in that city will send you a letter denying you further care if they find out you are having a homebirth). At first I thought he was going to drop me all together, which really would have been fine with me at that point because I felt totally comfortable with my HB MW and like you I was far enough along that there didn't seem to be any major issues coming up. In the end, he decided to continue seeing women who were planning on having homebirths on a "consultation basis" basically all the appointments that would have testing associated with them 12 weeks for heartbeat and labs, 20 weeks for ultrasound, 24 for GTT, and 35 for GBS, etc, (maybe more but I just can't remember). This worked out really well for me because I felt like I was truly making a fully informed decision, but didn't have to drive 45 minutes go to all the other worthless appts--IMO because all they did at those appts were the same things that my MW did--BP, fundal height, listen to heartbeat, ask if I had any questions, etc.
Anyway, to answer your question, I think those reasons sound fine. If you still do want to see the OB (for GBS? if that's something you want to know about) perhaps your OB would be open to this "consultation" relationship? Best wishes on the rest of your pregnancy and birth!