There is a large amount media in the market at the moment regarding the exceptions for skill gaming from the UEIGA that was recently passed by the US congress and then signed by the President. This Act specifically states that skill games are not covered by the Act.
Online pool for cash is a skill game by definition therefore it is not covered by the UEIGA and is legal in most states in the US. There are a few states in the US which do not allow skill games to be played online for money. A list of those states will be coming soon.