The problem you're likely to face with using an outdated third party toolbox with Matlab is that Mathworks occasionally changes how some functions are performed, which requires changes to how the inputs should be assigned and/or how the outputs should be used.
One of the bigger changes I can think of in recent updates is the graphics engine update that came with 2015b. I preferred the older graphics package at the time, but have come to appreciate the newer graphics. The big change that I noticed was that
pause) is required any time you want to update the frame (as in during animations).
Generally speaking, though, if you attempt to call a function that has had its functionality changed in an update, Matlab will issue a warning notifying you that the syntax for that function has changed.
If you're especially concerned, you can download (request trials if required, just tell them you're checking compatibility) versions along the way (2015a, 2015b, etc.) and check that your code works correctly at each instance.
I would certainly have a simulation pre-configured in a functional and known to be correct form first, and then you can check that the results are the same across versions and that the results are the same as what you get from the official toolbox.
As I mentioned in a previous post, the third party toolbox is for an outdated version of Matlab and hasn't been updated itself in years, so I would be reluctant to use it at all. If you're going to have the third party and official toolboxes installed simultaneously, then I would suggest you get yourself acclimated to the new toolbox by attempting to translate your existing "known good" work. Official toolboxes are maintained by Mathworks and you get tech support, too.
For the record, too, you stated you're using 2014b - the official Robotics Systems Toolbox was first released for 2015a, so you'd only need to upgrade one version if you're really concerned about compatibility issues. 2015b was the big update.