Metchosin: Yes, normally the tune alone was played, but I was referring to a submission to the page you linked (http://www.tvparty.com/lostgiant.html):

"I used to love watching Bob Homme as Friendly and Rusty and Jerome, and of course the rare appearances by those musical cats [Angie and Fiddle, two puppet cats, who'd play violins once a week].... Occasionally, they would perform concerts featuring the cats and of course the whole gang playing various instruments. I seem to also recall they even did a half-hour special, which was also a concert.

"The theme song from FG was 'Early One Morning', which they mentioned once during a concert was an old song from the 16th century (I think).... In fact, during the same concert where they gave the name of the theme song, they played the song and Jerome sang the lyrics to the song."

- Lynda VE

So apparently the lyrics were sung only once, if this person's memory serves.