He should def try it. Rowing is fun.
Physically, right now, he can concentrate on building on his baseline fitness from XC. Long steady runs. And add some conditioning to build leg strength and particularly core strength. A rower needs strong back and abs to support the whole body action of rowing.
Rowing is technical. He will need to be patient with himself and other novices as they learn how to row.
Rowing is time-consuming and a real commitment to the team. Getting to practice takes time, practices are long and you can only do so much training on your own. You really have to show up when you say you will. An eight can’t row if only seven rowers show up.
Don’t worry about going in the water. Someone will fish you out.