Yes Shutterfly mugs are microwave safe.
I have a Shutterfly Mug and have always microwaved it without an issue and even Shutterfly website says that you can safely microwave the Shutterfly mugs.
The Shutterfly mugs are made just like the other coffee mugs you buy that are ceramic and even those can be microwaved safely.
If you want to microwave your Shutterfly mug to heat up some coffee, tea, milk etc or whatever you're drinking from it and it will be just fine.
Shutterfly says right on the website that their mugs are microwave safe.