Thx Jimp.
http://forum.pfsense.org/index.php/topic,39627.0.html (same topic discussed here also, Jimp response more thorough)
@jimp:
It isn't "reverse" lookups in that way. You can add hostnames to an alias. Periodically, these are resolved again to ensure the IPs are up to date. They are used like any other IP-based alias entry.