A fringe player is somewhat less than an "Ersatzspieler" (or "substitute"), IMO, at least not the way I understand "Ersatzspieler/substitute" to be used in soccer where there's a limit on how may substitutes are used.
I don't know much about hockey (ice or otherwise), but I do know a little bit about basketball. Typically, an NBA team will have 13 or so players (usually one or two more before trading deadline). Of those 13, five will be on the "first team," i.e. they are the starters and usually the team's best players. Then there's the bench, or the 2nd team, consisting roughly of the same number. Sometimes 5 bench players will relieve all the starters and play for about half a quarter or so to give them (the starters) a chance to rest, sometimes only some of the second team will be put in the game. It all depends on how tight the score or how important the game might be.
At any rate, that usually leaves about 2 or 3 players that never get to play, for whatever reason. Maybe they're rookies and not ready yet, maybe they're just mediocre players whose only role is to bring their bodies onto the court during practice. Those are who I'd consider the fringe players.
But every once in a while, such as when a team blows out the opponent, i.e. beats them so badly that there's no chance of the opponent coming back and winning, the coach will let the fringe players get on the court and play. This happens only during the fourth quarter and tends to be referred to as "garbage time."
Most people don't remember the names of the fringe players on their favorite team, and they usually come and go without much fanfare.
I suspect, hockey might be similar, but I don't know if there's a specific term in German for that.