No, Locke was not Smokey.. Smokey was Locke. According to the theory, the Locke we saw in Seasons 1-4 was the real live flesh-and-blood John Locke. At the end of Season 6, we'll apparently see him come back to life and get thrown back in time. So that future-Locke/Smokey was on the Island when present-Locke showed up.
Look at it this way. Remember that scene in Season 5, back in Dharmaville, when Miles is standing outside of Dr. Chang's window, looking in? At
himself as a baby? Same thing.. Lockes from two different times are in the same place at the same time. Future-Locke knows who Past-Locke is, but Past-Locke doesn't. He just sees.. something. Whatever he saw that first time, it was NOT a smoke monster. Maybe he described it as "beautiful" because he literally saw something of himself in whatever he was presented with. Remember, he was quite surprised when he saw Smokey's "natural" form at the end of Season 1, and he was frightened. It was pretty obvious back then that Smokey presented him with something very different that first time they met.
I imagine we're going to see a answer-drenched flashback of Smokey before this show ends. Then we'll know for sure.
Oh, and can someone explain why I'm vehemently defending this Smokey-is-Locke argument? I thought it was bollocks until this week, and while there's a degree of probability involved now, I still don't really believe it.. lol. I think I'm just trying to get people to understand what the theory is and the confusion over Smokey-is-Locke, but Locke-is-not-Smokey.