Hello.
If we are talking about DMVPN phase 2, then the best would be to use totally NSSA, but in this case you have a problem with default gateway for local Internet breakout.
>>The site A router will have an adjacency with the WAN Provider DMVPN router who will be redistributing BGP into OSPF.
Sorry, didn't get it - does your remote spoke learn prefixes via BGP and does redistribution into OSPF? If so, it could be good idea to use iBGP in your DMVPN.
If you want to extend OSPF over DMVPN cloud, you could use NSSA, doing summary into the area on DMVPN Hub (for all your internal prefixes).
PS: full table on the spoke is not needed, unless you plan to have some other exit point on the site.