Single vs. Trebles
Ted is right: we often do not have the option of a treble for steelhead or Atlantic salmon in North America.
Here's a brief overview of sea-run Atlantic salmon regulations regarding hooks in North America.
U.S.A.: All fishing for sea-run Atlantic salmon is closed.
New Brunswick, Nova Scotia, PEI, Newfoundland, Labrador:
treble hooks are illegal.
Quebec: treble hooks are legal (last I checked, at any rate) but only in size #6 or smaller.
I don't know any anglers who fish trebles in Canada either with tubes or with the pattern tied on the treble.
For tube flies (not generally as popular for Canadian Atlantic salmon as for West Coast steelhead), most use either the Partridge Nordic Single--a black carp hook--or the Loop Double. I also use a Mustad 9174, a super-strong egg hook: cheap and very effective when sharpened.
Anglers still use a lot of doubles in Quebec, mostly Partridge and Mustad. I prefer the Loop Down-Eyed Double Hook to either of these brands.
Single hooks are more popular everywhere else. In Newfoundland, single barbless hooks are now required by law.
Offset single hooks may improve hooking very slightly in the situation you describe. I used to fish an offset Gamakatsu single hook. I no longer bother with offset single hooks and notice no drop-off in hooking-to-landing ratios.