Well, when I told my (otherwise very lovely) midwife that I thought I had SPD, she just asked if it was stopping me doing anything. It wasn't, and she didn't ask any questions to ascertain whether my self-diagnosis was correct. I've since got myself a physio referral - the pain's nowhere near as bad as some people on here, but I don't want to take the risk that it gets worse, and then not be able to actually get an appointment.
So I would say worth mentioning, but I wouldn't necessarily expect any notice taken.
There's some useful advice in the Pregnancy section on SPD dos and don'ts. Mine seems to have improved since I started sleeping with a pillow between my knees - don't know if that's coincidental.