By reverse nPath, I assume you mean the following:
client SYN to router with destination IP of the server
router sends SYN to server
server uses a route or default gateway to send SYN ACK to LTM self IP
LTM receives SYN ACK and responds back to client through router
router sends SYN ACK back to client
It's technically possible to use SNAT for reverse nPATH, but I don't think it would work as the client would have initiated a connection directly to these server IP address. So if LTM uses SNAT to send the SYN ACK back to the client, the client would reset the connection as the source IP wasn't the same as what it sent the SYN to.
Or am I misinterpreting your scenario?
Aaron