It is possible to connect facebook messenger to pidgin irc client, but is there a method to connect it with hex chat client?
Pidgin isn't an "IRC client". It's a multiprotocol client which supports the Facebook MQTT protocol alongside IRC (and dozen other systems like ICQ, AIM, Y!IM, XMPP, QQ...) Indeed it has a much stronger focus on chat/IM systems, and just happens to "support" IRC because it can. So when you log in to Facebook through Pidgin, you're not using its IRC capabilities at all.
Hexchat, on the other hand, is purely an IRC client. It doesn't support Facebook Chat, because Facebook uses MQTT and that's not IRC.
In order to use Facebook Chat through a pure-IRC client, you would need to install a gateway server which converts between the two protocols. The most maintained one is Bitlbee. Such a gateway acts as an IRC server and presents various IM contacts as if they were people on this fake-IRC.