This would certainly save a little bit of time (baggage delivery isn't super quick at Dublin sometimes) .. but I think (unless anyone with more recent experience can contradict) that you shouldn't assume you'll able to checkin online on AerLingus.com for a BA codeshare ticket so you will still need to be processed by a checkin agent at T2 in Dublin by ~0900 to get your boarding pass .. The first BA flight is due to arrive at 0805 in T1 .. first flight of the day for the aircraft so shouldn't be many reasons for a delay other than LHR congestion, but it looks as though that can frequently make that flight up to 15/20 minutes late .. that with slightly slow passport control and finding your way over to T2 and potentially having to queue to checkin puts you in dodgy territory quite quickly.

It's certainly doable, but it wouldn't take much to throw it off course so you'll be more comfortable coming over the night before .. Hotels in Dublin are cheap with the EUR exchange rate at the moment ( Depending on how many bags you'd be planning to leave at left luggage it mightn't be that much more expensive!!)