I didn't even know NISLT was a thing, but 475k subscribers and daily videos seems like a good option if they would be interested. I think the biggest growth area is noobs and fan-level people, who get psyched by seeing cool shit, and inspired to do it themselves. People who are already into comp probably want to concentrate on comp stuff, and I've even seen an attitude among those types sometimes that looks down on pure jump as dumb since "most of it doesn't help in comp".
I think if we are looking for some channel/s to team up with, for best results they should probably have noobish viewers tbh, rather than veterans who almost certainly know about jump stuff and have their priorities already established. I was going to suggest finding out who was the most popular tf2 youtuber who was decent at jumping, and pitching something to them, but maybe NISLT would be the best option out there. They get very good view counts, and seem to be targeted at a good demographic. Anyone have any insight on that channel or know siN who seems to run it?