Rowing machine is one of the few cardio tools I like. It works most muscle groups so it raises the metabolism quite a lot. Directly answering your fat burning question: yes it does, very well.
The only thing is it isn't the same as a weight bearing cardio exercise, so make sure you are still doing real exercises like squats and deadlifts.
Cycling isn't enough, ditto swimming, but running, jumping, and resistance training does promote bone density through increased skeletal loading. HIT? That has nothing to do with anything.
Tim has it spot on about the bones. yes there will be some bone mineral density improvement, but not the same as a weight bearing movement, especially for strength or power. The acsm has conclusive research for strength training building bone mineralization, but as for aerobic exercise, not much , if any.