According to this (songfacts.com link), it [u]is[/u] Steve Tyler singing. However, apparently Joe Perry does sing in concert, so I wouldn't rule out the fact that Joe Perry did at one time sing "Dream On" live.

There were some funny facts on the songfacts.com site about Aerosmith, like

• Ronnie James Dio sang this on the album Aerosmith Tribute: Not The Same Old Song & Dance (released September 7, 1999). Yngwie Johann Malmsteen played the guitar part - It's what you'd expect, a million notes per minute.
  


• In the 1970's, Grateful Dead guitarist Jerry Garcia called the band the druggiest people he'd ever seen.
  


• Aerosmith appear in the movie Sgt. Pepper's Lonely Hearts Club Band as the FVB (Future Villain Band). It is considered one of the worst movies ever, but they got to kill the Bee Gees.