Live minnows generally work well in slightly warmer water temperatures. Since most rivers right now are no more then 2 or 3 degrees the fish will prefer roe, beads, pink worms and the odd fly pattern. The live action of a minnow may trigger the odd bite from a rainbow but your better off with other baits. There is an exception, The Niagara River has warmer temperatures then most inland rivers and creeks and there is a large population of brown trout, which are the most aggressive and will tend to hit minnows more often then rainbows in the dead of winter. Gulp minnows work well because of there lifeless action, they simply tumble around and look like an easy target for a hungry trout. Having said all that if your not getting bit on everything else....try a minnow!
Good Luck!