Oh they know. Aer Lingus needs to spread it's wings (if you'll pardon the pun).
Aer Lingus being gvmt controlled is in a constant uphill struggle - whether it be Ryanair's takeover threats and gvmt funding issue or whatever else they face. Aer Arann is a safety net - allowing them to meet quotas to satisfy the gvmt and other shareholders and make better margins on the long haul routes with their fleet.
No doubt they know - but imagine Aer Arann becoming the national airline? I'd pity the country if it did.