To my knowledge, only Samsung and LG devices have an EFS partition. I have had HTC devices for quite some time and have never heard the term EFS before I bought a Galaxy S4.
The EFS partition holds all of the IMEI data, wireless hardware info etc...On HTC devices, we need S-OFF before we can modify radio data I believe. So HTC must have something similar, but I'm not sure it is specifically an "EFS partition".
But given how vital the EFS partition is to those devices that utilize it, I'd make sure it isn't there before I went tinkering around.