bad idea to reimplement XA Transaction handling just for two servers and one specific EJB client API, when you have a separate project specialised for complex problem like XA two face commit.
Typically you don't have just two servers for XA recovery but, often XA Transaction is spawn over TXT Datasource(s) which interact also with TX Manager from DB. Or if you have JMS Ressources like Queue or Topic with TXT Connection Factory.
What if Stand Alone Client is using EJB API to communicate to a Server A EJB , but this EJB calls Server B EJB over let say iiop...?
What if TXT start was issued outside of Server or if Serve A and Server B are back, but the DB is still down.. ?