There's a yuge range among Roman Catholics. He could well belong to the fundamentalist branch.
Of course but on the whole Catholics in America just aren't as scarily organised and dogmatic as the Southern IFBs. Ryan is pro-life and holds a similar position as the Pope in that homosexuals shouldn't be discriminated against or hated but shouldn't be married either. If he became president he would be very unlikely to allow people the "religious freedom" to discriminate and I'd be surprised if he tried to roll back gay marriage. He probably would be very likely to at least fail to protect reproductive rights and might well try to curb them.
As a Catholic he would be bigging up his appeal to the massive Irish American community which is generally quite conservative but again not as bad on the whole as the IFBs. He's already making a huge deal of his Irish roots, suggesting that one way or the other he intends to be president one day. But what helps there is that Ireland itself is now an extremely liberal country that wholeheartedly supports gay marriage and is fighting an important battle to increase reproductive choices. So someone promoting their Irishness needs to be a lot more middle of the road these days.