I believe that starting this year, OHP is only covering CNMs, and may not be covering homebirth at all. If it isn't already in effect, it will be very shortly. While CPMs have been covered under the OHP/CareOregon open cards in the past, that is no longer the case.
I would assume that the rules regarding open cards remain the same, meaning if you are covered under OHP/CareOR before your last trimester, then you would have a managed card, rather than an open card, in which case you would have to choose from OHP's managed physician network, rather than picking your own provider.
All that (discouragingly) said, many Portland CPMs are willing to work out extended payment arrangements. I know this is the case with both Alma's and Andaluz' practices. Also, if you have a flex savings plan, flex money can be used to cover the services of CPMs.
Sorry I don't have better news for you 
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