For those like me, stuck in this boat, I have whipped up a little AppleScript applet that lets you drag and drop one or more RTF files (or any text, actually) and it will be saved as HTML in the same directory.
Code:
on open filelist
repeat with i in filelist
do shell script "textutil -convert html -extension html '" & POSIX path of i & "'"
end repeat
end open