Depending on the date, you may be able to find him in one of the many Knightage or Peerage/Baronage/Knightage books that are available on-line. For example, a quick search on Google books came up with quite a listing, including an 1841 edition of Burke's The Knightage of Great Britain and Ireland. (I looked; Sweetlove isn't in there. Sorry!) But such volumes usually contain a fair bit of information on the individuals included, including genealogical descent in many cases, and so you might try some of these volumes to find this Sweetlove.
To answer your other question, though, yes, certainly, the Office of the Chief Herald in Dublin should be able to give you some kind of an answer if you wrote to them directly. (I've had the opportunity to meet several of the people who work there, and they are all very nice folks who will try to be as helpful as they can to inquiries.)
David