[Peacefrog]

A player can be non-medically redshirted at any time, once in their college careers, granting them an extra year of eligibility to develop. In real life, it generally only happens Freshman year, but it can happen later, so the game allows it at any time. Seeing the (RS) by a player's name means they've been redshirted in the past. If you're playing a Dynasty, the game lets you control who gets redshirted and who doesn't, before the start of every season.

To answer your first question, I believe players that show up on Edit Roster but not on the Depth Chart are players that are currently redshirted. Try going to a practice mode in a Dynasty and look at the depth chart there. You should be able to see your redshirted players. But be careful, putting those players into practice removes the redshirt designation.