Just wanted to add my experience with Tricare and homebirth.
I got pregnant in March 2009 and had my first appointment at the Naval Health Clinic around 11 weeks. I attempted to obtain a referral to the local homebirth CNM practice and failed miserably (the lady who does referrals gave me a schpeel about how dangerous homebirth is and "what if your baby has a nuchal cord!?!?!?") so I just filled out the paperwork to switch to Tricare Standard.
My care under the CNMs was 100% covered. I was initially told that birth center births were free, but that there was some kind of fee for homebirths. I never got a bill though so I'm not entirely sure what they were referring to (I also talked to two others who had homebirths with them and they were never charged for anything either). I was referred to Ft. Belvoir for my 20 week ultrasound so that was covered as well. The only thing that I had to pay OOP for was my birth assistant and she was $750.
For our next baby, I plan on using a CPM (just wasn't satisfied with the CNM practice) so she will be paid for 100% OOP. I plan on submitting the claims to Tricare and hoping that maybe I get lucky and they end up covering some of it. Their policy states that only CNMs are covered, but I have heard of women getting around that. Unfortunately it seems to hinge on either the midwife having a billing person who knows how to work Tricare's system or someone at Tricare overlooking the fact that the bill is from a CPM and not a CNM and accidentally paying out. Never know, Might get lucky :)