Do you need to provide current for trout that you catch in a lake? because there would be no current in the lake so why should there be current in the aquarium?
The main issue people have with trout is temperature - they like temps in the mid sixties or lower and really start to suffer at higher temps. A chiller is pretty much mandatory.
I can probably do 68 degrees Fahrenheit, I have tons of aerators and the little guy I'm catching I'm probably gonna stick in my 48x12x25 for now. Power head I can do 3200 gph.
They will be fine without current, oxygen definitely more important, especially when things warm up. Rainbows look great when they get bigger in a pond, they'll soon out grow most aquariums. I don't have rainbows at the mo, but do have a brown trout in my pond... Cool fish to keep.