I am wondering if I can use the Cree zig bee bulb with a GE zwave on/off switch. I want to have dim lights in the bathroom at night. I already have GE zwave on/Off and smartthings
Unfortunately, no. You should never use a smart bulb with a dimmer switch of any kind, smart or not, as the bulb and the switch will confuse each other and you can burn out one or the other. And if you combine the smart bulb with a plain smart on/off switch, the inrush current to the bulb each time you turn on the switch can damage the bulb over time.
Smart bulbs are intended to always have maximum current coming to them and then the bulb will decide for itself how much power to use. So just use regular dumb bulbs with your GE switches.
If For whatever reason you need some of the features of a smart bulb, such as color changing or color temperature changing, then you need a switch which doesn’t change the current to the bulb. See the FAQ (this is a clickable link)
I have Cree bulbs. They are screwed into light bulb sockets with no dimmers or smart switches. I like to dim my living room low when watching movies, normally under 10% down to 1%. I have a Cree bulb that will turn on at 1% when I run good morning routine. The Cree bulbs at 1% are still not all that dim. I can easily navigate see around my living room completely. My bedroom light seems very bright for 1%.
Another option might be using a very dim yet dumb night light and controlling it with a smart switch that controls the outlet. Some night lights are as dim as a low glow while others will light up a room fully.