Ive had pretty fruity beers pitching at that temp,if you like it then have at. I havent done that since my first few beers,which I think is way to high. You could get too fast a ferment as well as alot of esters. Ive always had good beers with nothing off hydrating at recommended temps then pitching at ferm temps. It does seem that you should add some wort after 15 min to ease it into your main pitch wort temp. Its really only about viability loss. So if you pitch more than enough dry yeast then you can pitch dry or hydrate and pitch the 20 degree difference and still afford some of the viability loss. Although it does stress and add loss of viability but again, if you overpitch you shouldnt have to worry too much about the temp difference. Although its better to strive for optimum yeast viability.
Also if your pitching just below 80 what temps does that mean your fermenting at? More than 10 deg drops can stress yeast(maybe more?) that way if you ferment in the mid low 60's that way. And its generally more estery fermenting above 70 to ferment in most yeast it seems anyway if your primarily fermenting that high.
So long story short: you may be getting more stressed yeast pitching @ 80 and fermenting above 70.
I dont generally hydrate- then add cooled(primary temp) wort- then pitch to main wort. I generally overpitch-hydrate, then just throw the hydrated yeast in to wort below or close to 70. If I knew I wasnt overpitching then I would add wort after hydration to get it closer to primary pitch temps.