Just for another point, I dry hop with pellets and I've never used a bag, but rather make a slurry, do a relatively quick dry hopping period, and crash cool, then transfer. I'm trying something new this time actually (going almost verbatim with what's been reported with what Black Sheep of Masham, England does - except they don't dry hop, and I will be), so we'll see. At any rate, with this regimen, fining at the same time, I always got very clear beer (I'm coming back after a long time away, but this was my prior experience).
On whether you should use yeast when priming, I'd think it's almost impossible for you not to have enough yeast to do the job. The only issue I could foresee would be a really extensive crash cool and/or cold conditioning period, followed by transfer. Even then, I'd think there'd be enough (though secondary carbonation would be longer). On the other hand, I know many actually prefer to use another yeast for bottle conditioning, anyway. One for the main fermentation, and perhaps another more attenuative, cleaner-profile strain.
I've never needed anything other than priming sugar, like everyone else is saying.