First, check out the following web page:
Involute Spline Engineering Drawing Data
This web page should give you an idea as to the spline data you need to reproduce the part. Also, I believe there are standard mill cutters that create involute spline geometry though hobbing is the best process..
To reverse engineer the component, I would first try to figure out what the part goes on. The OEM may in fact have engineering drawings or specifications available for download or other.
If you have a CMM then you already know what you need to do to determine the geometry. I would also know what the application is and try to estimate the loading as this will drive your engineering materials selection and any case hardening (like QPQ, Nitriding, etc.) you may need to do.
Of course you simply have a metallurgical done ($$) to determine the material