It is far easier to become a CRI than to become any of what traditionally used to mean a "flying instructor".
If you don't care about getting paid, you just need a PPL and a little bit of other stuff. Practically anybody with a PPL can become a CRI if they want to.
This is why an insurer might view it differently, and it is worth a check. Especially as it is normal for an insurance policy to allow any un-named "instructor" to be PIC, without any additional requirements. This means that somebody with a CRI could fly around in just about any aircraft (for which he is legal, regardless of experience) under the owner's insurance, without the insurer knowing anything about it.
A CRE is different; for that you need to hold or have held a JAA Professional Licence (i.e. a CPL or ATPL).