The walruses might be remakes of the http://www.uesp.net/wiki/Bloodmoon:Creatures#Horkers. Though they do look a bit different than the horkers. Perhaps they are just walruses.
Just because concept art exists doesn't always mean that their contents are confirmed. Where the hell was the Spider Mastermind in DOOM 3?
I'm sorry but given the strict manner and tight scheduling in which information is being released it's quite obvious they are taking great care (and have done so since FO3) with their marketing and they will not show us anything that they aren't 99% sure will be in the final product. That includes concepts.
The walruses might be remakes of the http://www.uesp.net/wiki/Bloodmoon:Creatures#Horkers. Though they do look a bit different than the horkers. Perhaps they are just walruses.
Maybe some relation, but I dont think they are horkers unless they completely changed the design. The horkers had weird mouths, while these have actual tusks and mouths that resemble a walrus. I personally think its kind of a weird addition though, so perhaps your right and they are horkers (or something else)