Silver Hatchet fish schooling with my bleeding heart tetras?

Hello - and thank you in advance for the help. I purchased 3 silver hatchetfish about a month ago. Unfortunately I have lost 2 of them - one found a tiny hole on top of the aquarium by the filter and jumped out and the other was ill. I know that hatchetfish are to be kept in a school (my understanding is at least 3). The hatchetfish that I have left is now schooling with my bleeding heart tetra school (6 of them). He is staying in the middle of the tank with them and seems very content. (It is funny to see him with the others though). I prefer not to purchase additional hatchetfish, but will if the fish needs this. I am wondering if any one has similiar experience with different types of fishes schooling with each other and if my hatchetfish is ok left as the only one in the tank with his 'tetra school'.