Quenneville said he was told the Blackhawks were under the $69 million salary cap with his current roster of 23 players, including 13 forwards, eight defensemen and two goaltenders.
"I think I got the word that we're definitely under, not a lot of room, though," Quenneville said.
Cumiskey and van Riemsdyk were longshots to make the team at the start of training camp. Blackhawks prospects Adam Clendening, Klas Dahlbeck and Stephen Johns were considered to be the front-runners for any defenseman openings.
The Blackhawks signed Cumiskey to a one-year contract in July. He played the last two seasons in Sweden after playing 132 NHL games from 2006-2011.
"Kyle gives us some speed," Quenneville said. "He's played a little bit in the league. He's got some exposure to it. Being away in Europe the last year or two, it's a different ice, getting reacquainted with the situational plays. But he has a great asset with his quickness and his speed."
Cumiskey hadn't been told whether he was going to make the team when he spoke with the media after practice.
"It would be very exciting," Cumiskey said. "I've had a rough couple years here. I've been looking forward to getting a chance to be back in the NHL. It would be a very special moment for me, for sure."
Van Riemsdyk was even less likely to make the team than Cumiskey. Van Riemsdyk signed with the Blackhawks as a college free agent in March after playing three seasons at the University of New Hampshire.
"Trevor is a young kid who really surprised us as far as how poised he was with his reads, his positioning, his patience and play recognition with the puck," Quenneville said. "So he had a good start, had an excellent training camp, is getting rewarded based on well he played in camp. Can he sustain that, what he showed us before? That's a big step for us and him as well. But he shows he's a pretty smart customer and cool in a lot of situations. We're looking forward to seeing him play."