You know that the many high schools in the northeast got into fencing because it was one of those things. I know a kid who got into Harvard about 4 years ago from NJ because she was a fencer. And my dog walking buddies who were going through college admission this year mentioned their top private schools were pushing the fencing.
So the admissions people at those privates must be on top of it.
Extended family member, who did undergrad at Princeton (played football there) then did MBA at Harvard was heavily invested in getting his oldest into Princeton. The wrestling coach told him that you can be off 1 standard deviation in the scores if you have the activity they want. Girls hockey or whatever.
Don't the schools have lists of all competitive teams? whether it is dance or fencing, they would look for that.