No.
They are 2 completely un related sports. Sure they have 2 wheels, sure they have a similar track, but its a completely different type of riding and VERY expensive.
Now adays, the avg bmx racer either quits (like so many of my expert and a pro buddies did) or they progress to Mountain Bike racing like I did. Downhill Racing is the extreme side of it, but 4x is always HUGE with bmxers now. Its basically downhill bmx racing. Its more dangerous. its faster, jumps are bigger, and way more adrenaline. I'll take my dh and 4x racing any day over motor x. Those guys are just lamers who can't pedal a bike IMO.
Here is a few different types of racing bmxers progress to. Now, let me just say, this makes bmx racing seem like a kiddy sport, and that's coming from someone who grew up bmx racing. The speeds are INSANE, everything is absolutely GNAR, and you have to be one hell of a rider.
NORBA DH
[ame=http://www.youtube.com/watch?v=JmXgNiHxlqE]YouTube - mt snow vt norba nationals 2006 downhill dh race dual slalom[/ame]
here is some dual slalom and 4x (downhill bmx but on mtb basically). dual slalom is 2 riders, 4x is 4 riders.
[ame=http://www.youtube.com/watch?v=VyrAq40c1xo]YouTube - Mt. Snow Downhill and 4X - 2006[/ame]