I'm not pro-doppler use, but I did actually rent one before (in my last pregnancy). It isn't hard to learn to use - no real learning curve, especially the further along you are (easier to find the hb). But I second the notion of talking these concerns over with your mw and asking to have her come in early labor just for a check, if that makes you feel better. However, consider what would happen if your dh *did* go to check for the hb and couldn't find it or heard something weird? Then what? You'd need your mw at that point anyway (and just b/c he can't find it, etc., doesn't mean it's not there - baby's position could make it very hard to hear). So I guess again I'd suggest that you just have your mw assume this responsibility. Oh, and fwiw, it may not have been easy to find a doula, cbe, or some other non-mw to assume this responsibility. I'm a cbe and have been taught to never do anything "medical" for fear of lawsuit should anything go awry (like if I can't find the hb but *think* the baby is fine but it isn't - I know this has been a problem for people in the past).
Mama to four remarkable kiddos, all born at home.