I haven't played on Bovada, but this their rule. Doesn't mention HUD's. HUD's are usually allowed on most sites.
6.3. No Player Assistance Programs. Use by players of external player assistance programs ("EPA Programs") which are designed to provide players with an unfair advantage over their opponents are expressly prohibited. We define EPA Programs as including computer software and non-software-based databases or profiles (e.g., web sites and subscription services) and we consider access to or the ability to gather data or information on other players by any means that would not be accessible via their own first-hand experience (i.e. observation of game play) to be "unfair". We reserve the right to close Accounts and void any and all winnings in such Accounts if we establish, in our reasonable discretion, the use of an EPA Program.