Nothing you propose to do is it bad, i.e you won't harm your beer by adding the hot sugar solution and or adding the Gelatine at the same time. So don't worry about that.
However; if your goal was to clarify the beer (adding gelatine) then the method you propose isn't efficient and you may undo the clarification process.
The best time to add the gelatin is right before you start the cold crash cycle, some people choose to cold crash it right down quickly others a stepped approach. Either way the gelatin is going to be most effective if added before the cooling cycle and allowed to sit for no less than a week.
Adding a hot priming sugar solution won't harm the beer (not in small quantities) but, if added to a cold solution and or relatively cold given the temperature differences it will cause a new haze to form in the liquid, the same way mist does when the cold ocean air meets warm land. Yes it does go away - but I have found it returns when you eventually cool the beer for drinking.
If clarification wasn't a goal for you - I say go right ahead and just add everything onetime hot or cold - but because it appears to be (given the Gelatine use) you want to be a little gentler in inducing any shock to the solution. If you don't have temp controlled fermentation to be able to cold crash then allow priming solution to cool as you have done previously before adding.