I was wondering if anyone has tried this before. I was planning to do them tomorrow but im not quite sure if the form would be different since im using the smith machine?
"stabilizing" muscles won't be activated due to the lack of needing to balance the weight, which is one of the greatest aspects of that particular exercise. i personally do said exercise holding DBs and i think it would be kinda difficult to have "good" form since the bar can only go up and down, feels to be that you need to be able to move "forward" slightly.
I do these with DBs as well.
I tried the Smith but didn't like it because it put my lower back into too much extension during parts of the movement.
Try it, though, and see if it works for you.
Just make sure your knee doesn't go forward. You'll have to focus on sitting back.