... is it possible to have it see the rf from my trucks remote start and send an x10 signal ...
As others have responded, it's not probable. The CM15A will report only 310MHz RF signals that match the signals sent from things like the HR12A or CR14A. Your truck remote almost certainly uses a different frequency and protocol.
But there's an even bigger obstacle - your truck remote surely uses rolling codes - if not, I can steal it and any like it by recording the RF when you start it and playing it back when I want to start it and drive it off to the chop shop.
If you are handy with DIY, you might be able to build something that would react to
any RF of the correct frequency. There will be an FCC ID number on your remote which you can use to determine its frequency.
Depending on the frequency, you can record the signals and then program a PIC or AVR chip to recognize the overall pattern and send a signal or activate a relay, etc. to accomplish your goal.
Might be easier to put a sound activated switch in the garage to open the door when the truck starts.