Yes he is allowed to ask a fee for his work. He did not change the compiler code.
And it is by all means a modest fee.
And yes, it is very useful for little sketches, f.e. to quickly test small examples for this forum.
I use the compiler as a cgi on my server now (as per what Jon did (L505)), but, yes it is very useful, but limited, as is the cgi solution btw.