Yes, it is possible that Tim Tebow is playing baseball as a publicity stunt. Although Tebow was successful as a college football player, he floundered in the National Football League. This meant that he could never fully reap the earnings from endorsement deals. His return to professional sports could help him raise money and fame through new endorsement deals, as well as the accompanying publicity of a professional sport player changing sports.
Micheal Jordan attempted to do the same thing after he retired from basketball, but it did not go well. Many athletes play multple sports when they are young and focus on only one when they become pros. Tim Tebow is likely trying to do the same thing and perhaps be more successful.
Tim Tebow like most Americans is out looking for his next job. I can't fault someone trying to work. Hopefully he is good at it unlike Michael Jordan. It's one thing to play on a regular ball field and be amazing, it is another thing to play on the professional level. It will humble any man quickly.
Tim Tebow's attempt to play baseball is not a publicity stunt. He is a good athlete and likely feels this is his best chance at playing a professional sport. He is young and probably would like to continue playing a professional sport since his football career did not pan out.