@neuroanatomist,
I purchased a BG-R10 from B&H in June. It came with a AUS/NZ Warranty card, same as your EL-5. I attempted to register it in MyCanon, but the listing for the item was not present. (Not in the product database). I called support and brought it to their attention. They agreed it was missing and said they'ed get in added. Somehow I was the only person who ever tried to register their grip in North America. (ok).
In the meantime, I requested an RMA with B&H. I claimed grey market. I'm in CA, so 11 days later I got my replacement. The exact same item (product) I had returned. It looked like they opened the box, put it in another box and sent it right back to me. I was pretty upset. Getting ready to leave for Alaska, took the time to exchange it and then this. This was the first time I hadn't had a stellar experience with B&H.
I actually got an email from Canon telling me I could register my product now. I logged back in and the BG-R10 could now be registered. It accepted the serial number too. I added my receipt. I'm not worried I didn't get a legit product or one that is physically or operationally different than US. All of my other Canon gear, lenses / body's have a US Warranty Card. As long as you can register the flash you should be good to go.