I've fed my poly a number of native species before, I haven't had a chance to catch any whitefish lately so I'm not completely sure but it should be fine. You'll want to make sure the lake where you're getting them from isn't contaminated, and as an extra step to prevent introducing any potential illness you may want to cook the fish before serving. It may be better to wait for a more experienced keeper before you take my opinions.
@loves severums Is that S. Petricola in your avatar?