The 6.5 (and 6.2) diesel is a 21:1 compression engine, and should not be running more than 11-12 pounds of boost to be a reliable and sustainable daily driver (the Commander turbo kit is calibrated for 10 to 11 pounds). This is generally considered to be a relatively low psi system, especially by modern diesel boost standards, where normal boost pressures can be in the 20 to 30 psi range, even from the factory.
With boost levels below 15 psi, an intercooler is generally not a worthwhile effort. The charge air is not hot enough to warrant the use of the intercooler. An intercooler actually acts to the detriment of a low PSI system, by adding turbo lag (due to the additional piping) and back pressure through the intercooler itself.
Regarding your charge air temperature question: The overall combustion chamber temperatures are several hundred degrees cooler with the introduction of the charge-air from the turbo; so the addition of the turbo actually helps reduce the thermal stresses on the combustion chamber components, including the heads combustion chamber inserts and pistons (as compared to the naturally aspirated 6.2/6.5 diesel engine), while simultaneously adding power and making the overall fuel burn more efficient.