There was a thread on the postgresql mailing list about the lack of XA support in the C API library (libpq). The conclusion of the thread is dangling which I guess implies that the support has not been added in the intervening years.
I thought all Narayana APIs except BlackTie are all Java based and XA is performed by the Narayana APIs. So can't we use PG Java API for transaction management?
Can we use Blacktie for ATMI calls and use Java based Narayana APIs to connect to PostGres and leverage XA?
Narayana can certainly be used with PostgreSQL. I thought you wanted to use postgres in the BlackTie side.
Are you trying to span a transaction from a C XATMI application into the application server where an EJB or similar updates a Postgres entity?
I have to use the atmi calls of blacktie. I will be using transaction related calls tpbegin and tpcommit of atmi. Will I be able to call these APIs and perform Postgres connectivity for this transaction via Narayana?
I am asking if I can use this as a workaround, since c API for Postgres is not there.
Sorry, I am still not totally clear on the "mix-and-match".
If you are saying can you start a transaction using tx_begin  (this is the spec compliant version of tpbegin) then call a Java service  which uses postgres and this Java service is hosted on WildFly then that should work.
Take a look at quickstart/blacktie/integration1 at master · jbosstm/quickstart · GitHub and see if it helps (the xatmi_adapter element of it seems to do (except the postgres side) what you are attempting. Using postgres from an EJB in WildFly should then work.