Is it considered caught out if the cricket ball hits the handle of the bat and nothing else and the ball is subsequently caught?
Yes. Quoting Law 33.1:
The striker is out Caught if a ball delivered by the bowler [...] touches his/her bat and is subsequently held by a fielder [...] before it touches the ground.
The handle is explicitly part of the bat, as defined by Law 5.1.1:
The bat consists of two parts, a handle and a blade.