No, you don't need to be a adwords subscriber. Something similar happened to us.
First of all, don't give up hope on your froogle feed. It took them nearly two months to get our items posted and that was after the feed had been approved by the froogle staff.
Second, froogle spiders the same as google does so sometimes your site will end up there even if you don't submit it.
We had not been spidered much by google before adwords, too. It came as a surprise to me when I found some of our pages in froogle before we had finished the submission feed process. If I had to guess, google and froogle may borrow from adwords as a jumping point for spidering sites. It kinda makes sense. Chances are, if you are using adwords, you probably are using it because you have certain pages that have not been indexed. In the intrest of the user, Google wants to index every page in the world. What better place to start finding unindexed pages than right within your own system.
If it were any other SE, I would think I was wrong b/c you could be subverting your money base but with google, they have frequently done this in the past so it would be no surprise if they were doing it again.
I am sure that googleguy will be along to clarify soon. :)