There are many reasons why search engines should accept such characters, but it appears that certain characters will make your pages take longer to index.
When i started building the HTML Reference, i tried to include less-then and greater-then signs in the title tag, to better name the elements. However it turned out that for whatever reason, those pages was getting indexed really show.
Try it if you must, but beware that your site might run into indexing problems on some search engines. The problem should however disappear when you remove the offending characters, and who knows, it just might work in your case.