Yes, you can access the BetMGM online sportsbook from the BetMGM site. You can also access the BetMGM online poker portal, too. Both are located in the top-left menu next to the BetMGM logo. 

However, both buttons technically take you to separate sites: and, respectively. While these are technically two separate portals, playing on any of the three BetMGM sites earns you points toward your BetMGM Rewards account, and many of the bonus promotions can be used playing at these sites, unless otherwise stated in the terms and conditions.