Can I use CAT5e jacks with CAT6 cable?

From Wikipedia:

Category 6 cable, commonly referred to as Cat 6, is a standardized cable for Gigabit Ethernet and other network physical layers that is backward compatible with the Category 5/5e and Category 3 cable standards.

You can always use a lower standard cable or jack, but you will be limited by the speeds of the slowest link in the chain.