As far as him running afoul of the "Roman Catholic church" ... he was the Roman Catholic church in Ireland for much of his career.
Actually, the evidence that Patrick made it to Rome to be commissioned by the Pope is rather sparse (this was the beginning of the (so-called) "Dark Ages" after all)--which many historians don't accept as authentic.
Celtic Christianity too, did differ on the holidays, and other customs (which were considered very important) and was not seen by Rome to be in obedience until the 600s, 200 years AFTER Patrick. The Celtic monasteries even sent their own missionaries, NOT under the supervision of Rome down into Germany, Poland, France, and even northern Italy. These monasteries and missionaries were not brought under the supervision of Rome until St. Boniface in the 700s.
The idea of Patrick as a compliant Bishop sent from Rome appears to be itself a later medieval historical revision...
http://www.americancatholic.org/Messenger/Mar2001/Wiseman.asp#F4
For most of Christianitys first 1,000 years, canonizations were done on the diocesan or regional level. Relatively soon after very holy people died, the local Church affirmed that they could be liturgically celebrated as saints.
That was the case with St. Patrick, whose feast has not been dropped from the Churchs universal calendar. Because it usually falls on a weekday during Lent, the opening prayer at Mass can be for St. Patrick, but everything else comes from the Lenten weekday prayers.