I am not sure anyone truly knows what it takes.
With that said, it is easier to define for a pitcher.
My view is velocity with command, and upside, defines being drafted for a pitcher.
None of the pitchers drafted from DIII this year pitched in Appleton. I believe four of them were from the SCIAC in Southern CA and only one of them pitched in the Regional. I would think a RHP needs to be 90mph or very close, with upside.
For position players, the first thing to know is the DIII stats are meaningless in the draft, in my view. No matter how imposing or impressive, they don't matter to scouts.
In our son's senior year, he had some gaudy numbers including 90 hits, a 42 game hitting streak, while striking out only 7 times in nearly 200 AB's.
I don't think those numbers mattered in his draft selection.
In fact, as many scouts who saw him felt he could not play at the next level as those who felt he could. For him, though, he generated interest and had a lot of scouts and cross checkers at games. It only takes one to like the player.
What matters are tools and upside that truly stand out on a baseball field.
Speed, arm strength, athleticism, versatility, bat speed, and skills with the bat, combined with getting much better each year in college can get a player noticed.
Getting better every year is important to show there is more upside.
A coaching staff getting scouts to look at the player also helps.
The coaching staff getting the player into top Wood bat leagues, and performing very well in those leagues, can matter.
Being a hard worker, showing a love and passion for the game can be the type of plus factors but only if there is speed, arm strength, athleticism and the ability to play and hit.
Our son was a DIII position player who did get drafted.
At the time, I didn't think it was such significant accomplishment. Having followed the draft since 2003, and seeing 20-24 DIII's drafted each year, with well more than 1/2 being pitchers, I now realize what he did getting drafted and performing at a high level in Milb was pretty darn good.