I don’t think we have any reason to believe that Regina was in hiding from Rumple…Cora didn’t need to hide her, as she’d gotten out of the contract (and possibly done some further mischief we don’t know about to Rumple–there still feels like some missing history). And let’s see…Cora was living a rather public life as Prince Henry’s wife (and thus we can infer a princess in her own right). Oh, and she marries Regina off, again, rather publicly, to a KING.
Rumple was probably quite aware of all this. Keenly aware. Intensely aware.
But he was clearly not aware of Zelena until he found her in Regina’s chambers.
Keeper of Belle's Gold magic, sand dollar, cloaks, purple FTL outfit, spell scroll, library key, copy of Romeo and Juliet, and cry-muffling pillow, Rumple's doll, overcoat, and strength, and The Timeline. My spreadsheet: https://drive.google.com/file/d/0B6r8CySCCWd9R0RUNm4xR3RhMEU/view?usp=sharing