Baking in a salt crust: What type of fish?
James Peterson, in his book Fish &amp; Shellfish, recommends char, blackfish, grouper, ocean perch, rockfish, small salmon, trout, steelhead, and striped bass, but not pollock.  However, he does say &quot;almost any round fish can be prepared this way&quot;, and pollock is a round fish.
I suspect that the reasons that you don't see pollock suggested for cooking this way, or for that matter any way other than fried, is because the fish has a reputation for being delicate, but also slightly fishy, and drying out easily.  So the risk of cooking it in a salt crust is that it could end up both dried out and extra-fishy tasting.  On the other hand, salt-dried cod is its own staple ingredient in a lot of cuisines, and pollock is closely related.
In my personal experience, freshness and quality count for a lot, regardless of fish variety.  If I had a couple really good, fresh, whole pollock, I'd probably try it, particularly if they are Alaska instead of Atlantic pollock.