If the press making the offer is reputable, even if it's small, yes - I would let them know that you have an offer of publication. Especially agents who are looking at your current MS. They may or may not be interested in negotiating a separate MS, but knowing that a potential client is being picked up by publishers is a good sign.
Make sure you do your research on the publisher though. It will not help you (in the agent search or in general) if they are a press that has questionable practices or is very new (unless they are founded/run by someone with significant publishing experience).
[I'll add. There's nothing wrong with small, royalty only presses. But they are not as enticing to an agent. And presses with no sustained history of publishing or sales are likely not to be a draw at all.]
Congrats! And best of luck.