Jesus founded THE church. If an unbelieving man were wandering alone in the desert and by chance came across a Bible, would he not be saved and part of the church if he confessed Jesus is Lord and believed in his heart, as Romans 10:9 says?
Calling Jesus "Lord" and doing works in his name, as Matthew 7 suggests, is not the same as believing he rose from the dead to pay your debt nor that you have accepted his generosity for doing so.
Either way whether you consider Arians and Mormons as Christians or not doesn't affect Romans 10:9. It is the most fundamental part of the bond that unites us as brothers in Christ and as the church.
The Deity of Jesus Christ is essential as much as his Life Death and Resurrection.
Not only is his Deity most evident in the Book of John but also in the letter to the Hebrews and the Book of Revelations.