Hi, Geison,
I think it is okay to connect ENC28j60 to a Kinetis processor which does not have ethernet controller. As you know that some of Kinetis has on-chip ethernet controller, which is a mac module, user has to use third party PHY. I have checked the ENC28j6 chip, it is a mac plus PHY.
If you use ENC28j60, the difficulty is software or ethernet stack. We have ported lwip ethernet stack for Kinetis family, we have rewritten the LWIP low level driver so that it matches with hardware Kinetis ethernet controller. If you use ENC28j60, you have to rewrite the LWIP stack, fortunately, the LWIP stack is third party stack, which is structural code, you just need to modify the file in the port directory based on the ENC28j60.
Hope it can help you.
BR
Xiangjun Rng