I don't race, so can't speak to that specifically, but I can say that aluminum frames are still very popular. They're not getting the ink they used to, having been superseded as the "it" frame material by carbon, but they're still very popular and often relatively inexpensive. As FormerBMX'er said, which frame material you choose is largely a matter of personal preference. Though different specific frames will demonstrate different characteristics, aluminum is generally thought on the plus side to be very light and very stiff (read "good for accelerating/racing") and on the minus side to be very stiff (read "hard on your bum"). (I understand design technology has been able to dampen some of the ride harshness in newer frame models, however.) Bottom line, aluminum is fine for racing under most circumstances. If the races will be over long distances, however, or if your nether regions are particularly tender, you may want to consider a different material.

I don't know anything about the Nashbar frame you posted the link to, but a lot of manufacturers make fine frames out of aluminum. I'd recommend finding one that is built up that you can test ride to (1) see how well it fits; and (2) compare to frames made of other materials. That way you'll be able to make a more educated decision.

Finally, enjoy. Picking the frame/bike that calls out to you is one of the most fun parts! Good luck.