Of course he is, writes Matthew Parris, marshalling evidence from across the canon--Captain Haddock, Thomson and Thompson, Professor Calculus, Bianca Castafiore, Chang Chong-Cheng, and, of course, Snowy:

In fact I can count only eight figures identifiable as women (about 2 per cent) from the complete list of some 350 characters among whom Tintin moves in his life. There are no young women at all, and no attractive women, in any of his adventures.

 (via Andrew)

--Christopher Orr