Thin, but 40k has done MUCH thinner… lol.
Why would Fenris even require a PD with The Fang right there on the planet?
It is considered a Death World and due to the Space Wolves recruiting from there, is 99% likely be immune to a tithe of troops for IG expeditionary work, as that would thin the potential for Astares recruits.
(sheesh I am surprised I remember this much of the 40k stuff…)
Might I offer an alternative that is 100% canon and a throwback to "old skool" Imperial Guard?
A detachment of Kanak Skull Takers.
link
They can match the orcs in ferocity, and MUCH prefer close combat. Most who tried to field these units used converted WHFB Chaos Marauders, no reason why you cannot use Frostgrave Barbarians instead!