Well, I think by that rule they meant that dwarves are asexual beings. Being asexual does not mean you don’t love in other ways–and obviously, the dwarves do have brotherly love for one another, and great love for Snow White, too.
Grumpy got sprinkled by fairy dust, which made him different, and gave him a special connection to Nova (who accidentally did the sprinkling). His situation is entirely unique.
However, we have another layer! All the dwarves have Storybrooke identities now–and presumably these were normal human identities. It is possible then that they -could- love now. (But, sorry, Whale, fairies don’t date any more than nuns do.)
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