I don’t imagine it would affect a language course where your teacher is properly credentialed.
Sure, if you ask your Osaka homestay mom to teach you Japanese, you’ll probably get Kansai-ben invading it even if she tries to stick to Standard Japanese.
But most teachers of Japanese as a foreign language learn how to teach Standard Japanese, and they know what proper Standard Japanese pronunciations and vocabulary are. My first ever Japanese teacher back in America was actually from Kobe (coincidentally only a few train stops from where I now teach), and she taught in Standard Japanese.
In your day-to-day life in Kansai (I live in Hyogo), people will generally not use pure Kansai-ben with you as a foreigner, unless you express some desire to hear it or something.