Collusion Betting in Bizarro Game

[Capt Phoenix]

I'm fairly new to Hold'em (been playing since wednesday) and ran into something weird last night.

After the $2-$5 Hold'em game broke up the only table left was what they called $5-$5 Hold em. State law mandates a $5 limit. This game has two $5 blinds, all the gambler types flock to it, and there are usually 7-10 callers to see the flop. Since I knew I couldn't pry my wife off the slots just yet, I decided (against my better judgement) to sit in and see if I could find a way to take advantage.
As I sat there playing so tight I would have hurt myself if I tried to pass gas, I noticed a strange behavior at the other end of the table. Two guys who were obviously friends would periodically go on these raising rampages. Every time the first one would raise the second would re-raise, then they would repeat it as the betting reached them again. They would do this before the flop and only when they had position, then (if the flop wasn't awesome) they'd repeat it after the flop. If that didn't work, they folded on the turn, or just check-called if they had mediocre hands. At the time I didn't think anything of it, and just filed it under "strange behavior to take advantage of if I get uber-cards".
It's only as I was reviewing the session today in my mind that I suddenly realized what I was seeing.

Was what they were doing illegal? How can it be proved? Should I try to spot it again next week, or just warn the pit-boss of what I thought I saw so he can be on the lookout?