Any prisoner can pray. But they can't hold a mass, give last rites or any other thing that religions require a clergyman to do. It does not seem unreasonable for the prison to spend a bit over $100K for multiple clergymen to come to Angola. They serve all the religions, not just the muslims.
Perhaps not specific to a particular religion such as Catholicism, but in general, some inmates can lead religious services. "Inmate-led religious programs require constant staff supervision. # Religious programs with Level I volunteers require constant staff supervision. # Religious programs led by Level II volunteers and contractors require intermittent visual and audio supervision by staff. This applies to both escorted and unescorted volunteers and contractors. # Special Religious Programs (e.g. choirs, concerts, seminars) require constant staff supervision." According to the DOJ, page 5. http://www.bop.gov/policy/progstat/5360_009.pdf
There is actually a baptist seminary at Angola and prisoners have been ordained in the Baptist church. But this is not so with Catholics, Jews, Muslims, and other protestant faiths. There are dozens of clergymen who perform religious services at state prisons. What they pay them barely covers their transportation costs. $120,000 annually for all of them.
The Catholic guy can pass another basket for a "Special Collection" every so often and not onlyeasily recoup those expenses but turn even turn a profit.