I ride English but after being thrown off by Sandie a few times recently, my confidence has definitely been shaken...so I've been riding in a Western saddle to get it back (just feel more secure than my tiny flat English "launching pad" lol). I, of course, am so used to the rising trot that I do it in the western saddle...and don't care how anyone else thinks I look!
I see nothing wrong with it unless you're showing Western I guess, and I know nothing about Western shows so who knows, it may even be allowed?? I say do whatever makes you comfortable!