I only have a small portable vinyl greenhouse but I do keep my cuttings in there. I do not cover them with anything because it's always warmer and more humid inside the greenhouse than outside. That's the purpose of the baggies, to create a greenhouse affect. So I would think they'd be unnecessary if they're already IN a greenhouse. I'd be afraid that in a glass greenhouse with glass bell jars there would be a chance that the cuttings would cook inside. Even in just morning sun all that glass will act like a magnifying glass.

I goofed up when I first posted, as hubby informed me that the greenhouse is not glass but polycarbonate.

As far as the cutting go, how long do I have to keep the soil evenly moist ?

Since I usually may not see how the root is growing or forming, I keep the soil moist until I see new growth from new leaves.

At that point, I still may keep it in shade until it has a few well-developed leaves, then I'll start the process to harden it off if I'm keeping it in that pot. If not, then I may wait a little longer for a well-formed root-ball (based on leaf growth), then transplant it out of its pot to a new location.

You might want to check out the Greenhouse forum. Lots of good information there. I start my rose cuttings in a homemade hydroponic set up inside the shed (see Hydroponics forum). Once they have roots I transfer them to pots and then move them to the greenhouse in winter. I have tried ALL the rooting methods and that one works best for me.