While Ryanair do appear to bare a spite for Aer Lingus and Easyjet I think they don't regard Aer Arann as worth being bothered about. Also Aer Arann only operate on the thinner routes that Ryanair can't, for example Galway-Edinburgh or Waterford-Manchester but not Dublin to either destination, thus avoiding each other. Indeed I would have thought that buying Aer Arann would have made more sense than trying to buy Aer Lingus but that's another story.
Ryanair and Aer Arann have peacefully co-existed at LDY for years and FR have shown no interest in the Aer Arann DUB route.
Ryanair effectively no longer operate to MAN, have pulled LDY-BRS and have shown no interest in LDY-EDI which they possibly could have, but given that they don't even have a daily PIK-LDY now, I doubt they would be interested.