I think the bad news here is that we have enough national approval polls and the result from last year to be almost certain that Trump's approval in Nevada is worse than this poll indicates. That suggests this was a fairly Trump-friendly sample.
I mean, this has Heller as less popular than Trump and Trump lost Nevada to Clinton. Why would Heller then be able to beat a halfway competent candidate tailored to the state?
Well also more people seemed to respond one way or the other when asked about Trump instead of Heller, so it might be worth waiting to see how Heller's ratings go as the campaign continues.