AFAIK, strictly speaking it's illegal to take bets on a licensed premises but I suppose a blind eye might be appropriate given the circumstances.
Yes you are correct, a publicans licence is one thing, a gambling licence is another and never the twain shall meet.
I remember having big problems back in the day fer a Bookies licence fer a new city shop because the shop unit previously had a historic publicans licence, even though it had long since expired it took months to get sorted.
On the other hand I myself did exactly as what you suggested above and went to a suburban pub many years ago at the proprieters request and took bets all 3 days during the Cheltenham festival, no till, no computer, just a bunch of dockets, a table, pen and paper and a cash float.
We also converted a Barna shed to a Bookies office at Cork city football stadium with similar tactics but someone
(Paddy Puker) objected to the Gardai and we were closed down after a few weeks.