Yes that's Ulag. Read his journal about the Apotheus Armor and how he used Sleeping Tree Sap to make the most flexible armor Tamriel ever saw. He talks about how Eorlund and Him were on equal standing so there, theres one orc who can do it, and so can Dushnamub
Your argument still falls flat. Ulag, even if by his account is as skilled as the Grey-Mane, is dead. That doesn't change the fact the Skyforge would remain empty. Plus, by equal standing, I think it's more, he was the only one who could make that flexible armor, which is comparative to Grey-mane being the only one who can craft Skyforge Steel.
And I see Dushnamub is more a Warrior than an Master Blacksmith. Again, nothing indicates he knows how to make Skyforge Steel. It has to be taught, and the only one who knows is Grey-mane who if captured, cannot do so.