am a trainee doula...but VBAC is my specialist subject, as it were
firstly, a doula is not there to monitor you, or to do anything clinical....signs of scar rupture can be picked up by someone who knows what to look for, and definitely by a midwife.
the odds of rupture are really quite small, but obviously it is a risk..but for me, it was a risk worth taking.
there is a good article by mary cronk about signs of scar rupture. will try to find it.
the main role of a doula, for a VBAC, is to keep you strong and supported when you are in the throes of it, to gently remind you of the end goal of labour....
did you labour at all with your breech, or straight to elective?
i think virtually any doula would be able to support you, as it is the continuity of care, the support before, during and after labour the that is key
a doula works with you before the birth,to know your birth preferences , hopes and fears and communicate those to the care giver, and to protect you when you are vulnerable
so in some ways , a doula would not need VBAC experience per se, to give you those things...IFYSWIM