No squirrels cannot climb PVC pipe.
That makes PVC pipe a good option for putting bird feeders on to keep squirrels off and away from the bird feeders.
However if you place the bird feeder with PVC near a tree then the squirrel may try to jump to the bird feeder so make sure to keep the bird feeder away from the trees.
You can also put some grease on the PVC pipe which also makes it harder for the squirrels to climb the PVC pipe as well.
The grease will help keep the squirrels off the PVC pipe or anything else because the grease makes it slippery and makes it impossible for the squirrels to climb.