Answer:
No. In the novel she is just a child, while he is an adult. The tea party ends with her storming off angrily due to his comments and him not even noticing. Clearly not love.
Though the newest movie does seem to hint at this, Johnny Depp, who of course played the Hatter, said that he viewed their relationsip as more of a brother/sister one.
Of course fans can interpret relationships however they like, but there seems to be no canonical evidence that they are in love.
In the newest movie, I believe he is. He gives himself up to the Red Queen so that she can be free, he gives her loving looks, and wants her to stay in Underland forever. In the tea party scene of the newest movie, he sits there and it looks all worn and dull in the scene. Its as if he has been sitting there , forever, waiting for her to return and bring back the happiness that he once had.