I have tried doing all sorts of things, even wrapping the unicode inside html tags, i.e. html∠</html>, but MATLAB converts < and > to its web-compliant string as well if these are anywhere other than in a "comment" line. I guess the html markup only works inside a line that starts with % (comment lines).
The only solution I can find is to post-process the html files that MATLAB produces. I have these 3 lines in a DOS batch file (and Perl installed on my PC). These work for the 2 symbols I really want just now. I guess I will need to add more lines if I add more symbols. Ugly!
for /f %%a IN ('dir /b *.html') do perl -pi.orig -e "s/∠/∠/g;" %%a
for /f %%a IN ('dir /b *.html') do perl -pi.orig -e "s/Ω/Ω/g;" %%a