HDMI is free from electromagnetic interference (EMI) to a certain extent, but the length it will carry a full bandwidth signal (1080p) will decrease as a function of the total induced electromagnetic field(EMF). if you think your HDMI might pick up significant EMI, you should use baluns and run 2 CAT5 or 1 CAT6, depending on the balun. the shielding and twisted pair construction should do better than an actual HDMI cable when dealing with EMI.
if you opt to use HDMI cables instead of baluns, extron makes highly shielded pro HDMI cables that should do well in a high EMI environment:
[Link: extron.com]