I've looked at the healthy extras listing online and they arent specifcally mentioned.
The only ones that are are these:
2 Mini Babybel Cheeses
3 Mini Babybel Light Cheeses
2 Mini Babybel Emmental Cheese Portions
I'd be inclined to think that 2 cheddar babybel would probably be fine as a healthy extra, same as the regular and emmental cheese varieties - after all, you can have regular cheddar as a HEXA and I cant imagine there is that much of a difference in the calcium content between a regular babybel and a cheddar babybel to mean that one is allowed and not the other.
Thats only my interpretation though, officially its not listed.