A 4.8 electronic 40 is slow, but lets compare his 40 time to Combine participants from this year and last. This year out of 32 RBs timed only 7 ran a sub 4.55 electronic 40 at the NFL combine. 1st round picks Knowshon Moreno ran an official 4.63, Chris Wells ran a 4.59.
Day two picks: Gartrell Johnson ran a 4.75 (4th rd.), Shonn Greene 4.72 (3rd rd.), Jeremiah Johnson 4.67, Javon Ringer, Rashad Jennings, Chris Ogbonnaya and James Davis ran a 4.6 flat, Glen Coffee 4.58, Bernard Scott 4.56.
Last year Mike Hart ran a 4.67 at only 5'9 tall and was a 5th round pick. Here are other notables drafted who didn't crack 4.6: Lex Hilliard 4.68, Ryan Torain 4.64, Marcus Thomas 4.6. Brandon McAnderson of Kansas ran a 4.9 at the NFL Combine in 2008 and ran for 1,000 yards in 2007 for Kansas! In 2008 Yvenson Bernard (who was a very productive college tailback for Oregon State) ran a 4.83 at the NFL Combine.
Also we must note that "fullback" LeRon McClain ran for almost 1,000 yards for the Ravens last year and ran a 4.88 electronic 40 at the NFL Combine in 2007.
The combine electronic 40 time average for tailbacks last year was a 4.56 and this year was just above 4.6.
If Emert has the intangables, powerful legs, tailback's vision, heart etc. than why shouldn't he be considered for a college power tailback? I'm not saying, necessarily, that he will be a good tailback and I would say that his H.S stats don't really stand out, but his 40 time shouldn't automatically disqualify him from running the ball in the FBS.
In the NFL- basically any guy getting carries at tailback in the last 20 years (other than LeRon McClain) runs a sub 4.8 electronic 40, but I have shown here that that is not the case in the FBS (Yvenson Bernard etc.).