[Thanks Karsten — here you go:]
I maintain a compatibility list here:
https://fcpxtemplates.com/fcpx-motion-compatibility/
There are also instructions for "backdating" a Motion template to work with older versions of Final Cut.
As long as there is nothing in the template that FCPX won't "understand", you should have no problems. Example of something FCPX will have a problem with: 3D Text in all versions of FCPX before 10.2. There are occasionally new features in Motion that will cause incompatibility with older versions of FCPX, like the Fill filter, Shapes that use Size/Width and Height (older versions of Motion used individual control points) and a very few other things like this (they're usually mentioned in the Release Notes — and you'll find links to those pages on my page.) So far — following the "rules" I outlined, I've had a 100% success rate backdating templates to an appropriate former version of FCPX. I have to do this on a one by one basis working with somebody else since I always stay "current" with both FCPX and Motion.
What happens if you backdate a template and there are incompatibilities? No more than you're experiencing now. FCPX will simply not let you use the template, or if "marginal" you may experience something that won't work right in the template. FCPX won't break [so far, in my experience]. It's worth a shot.