Neither Scotland international has recovered from injury in time for this weekend's game against Lions, but Smith described their prospects as "50/50" to face the Stormers.
Horne's absence was keenly felt during Glasgow's Champions Cup defeat to Toulon, while Cummings' potential return would be a major boost in the second row, where the Warriors are currently stretched for options. Both players have travelled with the squad to the South Africa.
"George and Scott Cummings are here," confirmed Smith to Scotland Rugby News.
"Both of them are 50/50 at the moment. Scott had a bit of a setback just before we flew - on Friday before Toulon, but we were already committed to him coming over. He's still progressing well, but it allows him also to find his feet.
"He's been assisting with the lineouts a little bit and getting some detail done now on tour that we have more time to do. It's good to have them both here. We'll see how they come through the weekend."
Smith also played down concerns over Matt Fagerson after the back-row forward was ruled out of the Lions match, suggesting the decision was precautionary rather than due to a serious injury.
"He had a tight hamstring going into last week's game," added the Warriors head coach.
"We've managed him this week. It's important going forward. There are seven games still left if you are involved in every one of them. That's a lot of rugby still to be played. I know we all want to win the next one, and the next one, and the next one.
"But you must also look at how we're going to get the best out of the players and have them fit and ready and fresh to contribute at max. It's 50 per cent management. Obviously, there was a bit of indication of a slight hamstring sensation that he had before last week. Hopefully, it's not too bad."
Elsewhere, Jack Oliver will make his first Glasgow start at scrum-half, while academy prospects Dylan Cockburn and Ryan Burke have been included among the replacements as injury pressures continue to test the squad's depth.
With only Alex Samuel and Jare Oguntibeju currently available as senior lock options, the inclusion of Cockburn and Burke underlines the club's current challenges - but Smith views it as a valuable opportunity for both young players.
"I'm excited. It's a massive opportunity for us to continue the growth. We know going forward we're going to need everybody. And we have shown that we've used everybody and needed everybody's contribution this season.
"This experience for them will be massive. It's a tough challenge to play the South African teams here as it is. And now for them to experience that early will serve them well in the future and specifically going into next season.
"We specifically worked hard with them because we knew we were going to need them. At the beginning of the season when I had the coaching group together, I told them the way forward is that these young boys need to be challenged. They must work hard in the gym. They must be technically challenged, and they've embraced that."