They definitely do share traffic. The Prima Poker sites (Royal Vegas, Crazy, Poker333 etc) do the same thing. They run the exact same tourneys. It's pretty much one big site.
There are however, some exceptions. The tournaments under the "special" category are usually exclusive to that site. I am pretty sure things like the College Poker Championships only run on
Royal Vegas Poker and not the rest of Prima Poker Network. The other sites have their own special tourneys that they run as well
I am pretty sure the iPoker network is run the same way (Noble, CD, BetFred,
Titan, etc.)