Well! I've got this:
They're gribbly little scavenger techno-barbarians
Basically one of the main guys in the Thorn Moons Crusade has probably the most awesome Space Wolf army I've seen, which has been a real inspiration for me. Here's one of his kickass models:
The Iron Sleet invitational is about the human 'regiments' that have mustered on either side of the conflict.
My take on that is as a fleet of 'crows' that loiter around the Space Wolves fleet, scavenging from battlefields the Wolves have swept through. (That's the gribbly little guy peering under the wreckage for widgets and doodads).
However, like Odin's Ravens they act as spies of sorts so the Wolves tolerate them. They've got a scavenger's curiosity, and the cawing chatter between their ships alerts them to points of interest and enemy defences and the like...
So yeah! That's the plan