JuankiMan said:
But no matter what he knows and what he can do, the only thing the Imperium cares about is that they're Ratling so they'd better shut up and give thanks that they're given the honor of fighting for He Who Sits On Terra.
That is the apparent canon position from the IG Codex - they are recruited as snipers, some doubling as cooks. No other official capacity is offered.
However, the IG Codex does not state that this restriction is a mandate from the High Lords of Terra. Therefore I am suggesting that there is wriggle-room within the GW canon here for OW to use. This Ratling restriction could be softened in the interest making Ratlings more interesting as PCs within OW. It might be generally the case that 95+% are snipers, but particular regiments in the vastness of the Imperium might train Ratling recruits for other supporting roles. An absurd and outrageous suggestion?