Very few anti-tank weapons are heat-seeking. Even the majority of air-launched anti-tank missiles are either camera guided or laser guided. Heat seekers for air to ground attack aren't very common (I honestly can't thing of any).
And for the most part, man-portable anti-tank weapons are line-of-sight weapons without guidance - specifically RPG's with dual explosive systems for penetrating armor. Most vehicle mounted anti-tank missiles are Wire-Guided with a visible light video camera, though some systems have cameras that can work in infra-red - but wire-guided weapons aren't self targeting, there's a man watching a TV screen steering it.
Also, Chameleon tanks would still look like a tank in NVG and normal visual systems (non-IR). So in a conflict like Iraq or Afghanistan, having IR Chameleon armor wouldn't help at all. I wouldn't expect too many insurgents have IR imaging capability. NVG would be much more prevalent. Since they're identifiying targets visually, a vehicle that appears like a car or just invisible in IR, but is still obviously a tank when viewed through NVG, is going to get shot at just the same. In daylight it's not even a concern as insurgents are just going to identify it visually anyways.
This kind of IR masking is really only good for avoiding initial discovery* from an enemy using IR imaging only, with a ruse that's likely not to hold up for very long. It might buy the tank a few extra seconds
in certain situations, but most times it would just be a non-factor. Though in Tank combat, a few extra seconds can be the difference between life and death, but the certain situations where it actually gains you those few extra seconds would likely be so rare as to almost never be a factor.
Considering that this system is likely very expensive, I just don't see it being worth it. I can see it being much more useful as a visual Friend-or-Foe identification system, than as a type of effective concealment.
*Of course though, for forces not in a vehicle (on foot), the sound of the tank would give it away long before detecting it by IR would be necessary. Tanks aren't exactly very stealthy.
