No there is no need to puree the fruits and vegetables. In fact, pureeing the fruits and vegetables forces the gliders to eat more of the insoluble fiber than they need.
Gliders often chew fruits and vegetables then such out all of the juices - then spit out the insoluble parts in neat little moon shaped 'spitlings' that you will find in the food dish and all over the cage.
They will get used to eating the fruits and vegetables. The fruits and vegetables are still new to the gliders so it may take a little time for them to learn to love them.