Yes, the internal driver is 4 ohm. There have been a ton of threads that can explain this better than I can. In a nutshell, there have been many reports from people running this combo at 2 or 2.6 ohms without issue, although Mesa doesn't recommend it.
If you are planning on running this combo with an 8 ohm external cabinet the majority of the time, you could buy an 8 ohm speaker for the scout, available directly through the Mesa site.
I run my 15" Mesa 4ohm combo and 4ohm cab all the time. Been doing it for several years and ridiculous volumes. I know the OP can't really recommend it but I certainly can. And I don't have a dog in the fight.
I recently sent the head to Mesa for a freshening up and the bench tech mentioned nothing about excess wear on the amp. A good cleaning and a strong bench test and she was back out the door.
Others are welcome to chime in, in case I'm giving out incorrect info. The 4 ohm is the main default configuration for the Walkabout Scout. If you buy one new, it will be 4 ohm, unless it was specifically ordered to be 8. If you are buying used, you will have to ask the seller what speaker it has, if it wasn't mentioned in the somewhere in their item's details.
I am located in Brunswick, GA which is the approximate midpoint between Savannah, GA and Jacksonville, FL.