Elvis was allowed a two-month delay, originally January 20, 1958, for his Army induction in 1958 due to filming King Creole. He was inducted on March 24, 1958. It is doubtful he would have been able to make the Rio Bravo shooting schedule
(May 1, 1958 - July 23, 1958) anyway.
I think Elvis did a good acting job in several films, particularly King Creole. I find him very pleasant and charismatic in Blue Hawaii and many of his other films. I believe his acting is completely adequate.