The Coalition force included 141 Hobbittm units (according to a count made one turn before the main assault on Gobwin Knob), led by Georgia Power, who also represented Hobbittm in the Coalition's war council.Erf-b1-p086
Like all the forces of the RCC, it is assumed no units from Hobbittm survived the destruction of Gobwin Knob.
Hobbittm may have been responsible for providing more siege,Erf-b1-p118 accounting for its small overall numbers but important role in the coalition, in much the same way that Transylvito and Jillian's Barbarian sides were small but critical contributions. Evidence for this includes the Blue Warlord being the one to comment, "We lost 40% of our siege," and commanding the siege forward after Ansom assaulted the walls, and the Hobbittm troops having picks and shovels. Whether or not this is the case, the bulk of the Hobbittm force (at least, after Parson's dwagon raids on the Coalition siege engines) seems to consist of blue-liveried infantry.
Shawn Bawn may have been a Hobbittm caster before being (unintentionally) killed by Charlie, given the Boromir signamancy and his fellow hobbit-like caster.
Real World References
The estate of J.R.R. Tolkien is known for zealous pursuit of copyright infringements. Thus, "Hobbittm" is a sarcastic nod to hobbit™, in an attempt to pronounce the trademark symbol. It also sounds like Hobbiton, one of the main towns of the Shire.
Tolkien's hobbits live in homes that are dug out of hillsides. This may account for the Hobbittm troops' use of digging tools against the walls of Gobwin Knob.