I asked a good friend in the Dept. of Finance about that, and the answer was - no, they won't. Checkpoints targeting dozens of drivers is one thing, responding to a tip-off is another.
Too much hassle and not enough return (a few hundred € in taxes - IF the owner doesn't decide the car's not worth the bother).
I'm looking to buy a car and except for my excessive sense of patriotism, I'd only be too glad to pick up a cheap number in NI or GB. So I'll just suck it up and scowl at people less patriotic (or stupid) than I.
How can someone in the Dept. of Finance tell you what the Revenue Commissioners and the Customs & Excise section do?