Can I safely serve raw beef roasts that were left out to thaw for several hours?
No, you can not safely eat it.  See answers to "Can I safely cook a steak that was left out raw for 7 hours".

Thawing at room temperature in air allows the surface to reach and maintain an unsafe temperature for some time, even as the interior remains quite frozen.

The appropriate ways to thaw the roasts are to do it in the fridge, or fully immersed in a bowl of COLD water with a trickle of cold water running over it.  Thawing in water is the faster approach, and often takes under 30 minutes.  It is safe to use this method for thawing requiring for up to 2 hours, but if considerable preparation is required, an hour is a better rule of thumb. 

These are the approaches endorsed by cooking schools and health boards.