Maybe this will help:
We , College Select, use nomination forms as well as letters/calls of recommendation. I cannot speak for others but I am sure they do pretty much the same.
We also get players via coaches recommendations and scouts recommendations-- we ask for a letter of recommendation from HS/Summer Coach and or pro scout--- I agree with "buckeyefan"--not every good player has been seen by a pro scout and thus cannot get a recommendation.
You never know where you will find a kid who is a "player" but you can get a pretty good idea before he arrives at the showcase.
There are various means of getting a " feel" about a players talent--- we have even had players teammates recommend a player to us and this is usually a pretty good barometer of a kids talent.
Hope this helps you
TRhit