Its perfectly OK to use zip ties if you first wrap the steel tubing with a cushioning tape, like the silicone rescue tape. I think it makes a much neater installation (I realize I could have done a much neater job of applying the tape) than a bunch of adel clamps all over the place. Just a personal opinion.
I think by splitting the firesleeve and then zip tieing it closed would drastically reduce its effectiveness in cas of fire.