Is it okay to view my recommendation letter once I've been accepted at a college?
Why would you ask to see the letter? If the professor in question tells you it was extremely strong, I presume you believe him. Asking to see one's letter after waiving the right to do so is a strange request, and doing so conveys an ignorance of or insensitivity to the norms of the profession. 

I would be taken aback if someone asked me this, and would also feel very uncomfortable either refusing or agreeing. Why strain what seems to be a very positive relationship? It is certainly not worth doing so simply for the idle pleasure of reading flattering things about oneself written in another's hand.