Thinking about getting on board with a UTEC. However, I'm hearing the UTEC cannot compensate for temperature changes or does not have the capacity to do so.

If this is the case, is there a solution? If not, do the current UTEC users on the board retune with every season?

The current WRX firmware has temperature correction with a resolution of 10*C between 0*C and 60*C. The STi firmware currently does not offer this, but probably will (I hope) in the next release.