I would say since this is a lightning protection system the NEC would not directly apply, but NFPA 780 will, Taps are allowed but there are requirements in 780 that would have to be adhered too.
If you are not UL certified to do lightning protection systems then you can be opening yourself up to a whole bunch of liability issues, and some that might not be covered under you liability insurance policy.
Many try to get into this work without checking what it takes.