If the application is for a short distance (<10 meters), there won't be any long cabling or additional loading that will need to be considered. If you terminate properly for the CAT5 cabling using 100Ω resistors you will end up with a RL equivalent of 50Ω compared to 60Ω for normal CAN cabling. Usually the RL parameter is from 45Ω to 65Ω, but you will want to double check this in the CAN datasheet. Also, be careful of the number of nodes you add onto the CAN bus, each node adds input resistance and the node will be in parallel with the termination resistors; be sure to not surpass 33 nodes and the 100Ω termination shouldn't be a problem.
Regarding degradation, if the CAT5 cable is terminated properly using 100Ω resistors, there should be no degradation. Differential o/p/output drive is well within the CAN spec at 50Ω load. So, there won't be any issue at this loa w.r.t. output voltage swing/drive.