The fox trot is an easy gait (see the Gait Chart) that many Icelandic Horses can do. If he can trot and can tolt, it is within his ability to fox trot.
Fox trot is not the same as a "trotty" tolt. A trotty tolt is still a rack where the timing is a little off to the diagonal.
Here are a few pictures of Icelandic Horses in fox trot, some at liberty and some ridden.