Yes, it is a great idea to learn how to do techniques with your "weaker" or less dominant side. Parkour is about flowing through and adapting to your environment, so you should always be prepared for anything that may come up. If you need to get somewhere in a hurry, you can't afford to come to the obstacle, realize you're using the wrong side, and then waste time switching to your more comfortable side.
       I would recommend that you take time to practice different movements with you less-dominant hand, just to get the feel. In fact, whenever I am practicing a specific movement (trying to perfect the form, working with different approaches to it, trying to find the flow) I usually do about half with my dominant hand and half with my lesser hand. It's a great way to improve your adaptability and strengthen your less-dominant hand.
 

That is actually a Tai Chi Chaun principle, for everything you do on one side you must do on the other. "An unbalanced body is an unbalanced mind." Obviously nowadays it's a lot harder as you write left or right handed and forget the other side and it's the same with sports like tennis, baseball, golf etc. but it's always good to be able to do things both ways.

its kinda weird.... i am ambidextrous  and I it feels comftorable for me no matter which way i use the the shoulder...