Observations:
1. Twitter accounts can be monitored by CBS.
2. I'm not aware that airline bookings can be made on Twitter.
3. In pre-Race sequester, CBS can certainly supervise Tweeting as a means of keeping casting and filming plans hidden as much as possible.
4. CBS and WRP can do these things using their contestant contracts, and the (alleged) five million dollar penatly clause in the contracts.
5. There was a time when I-pods were banned too, but that did change in more recent seasons since the content of the I-pods hard drives can be checked electronically.
Bottom line -- The use of a Twitter account, in and of itself, may not prove anything.