See vt, iwx, and some others.

Would we need to load this in early boot instead of rc.conf?

This has no kernel tunable options or sysctls?

Since this is a freebsd driver, freebsd is redundant here.
Roff needs one sentence per line.

Can it just mount and access them? Is creating possible?

+ .Pa lets people use apropos Pa=sqfs
+ putting the root prompt breaks copy paste and is implied for mount, you typically only want to use them for a complex multi line example where only some parts should be ran as root.

No blank lines in Roff

Du-oh!!

I could imagine both needing this driver at early boot as well as later in rc.conf

And correct, no tunables or system controls at the moment.

Does this work better:

The squashfs driver provides support for mounting and accessing SquashFS compressed file system images.
SquashFS is a compressed read-only file system designed for general read-only file system use in constrained block device/memory systems.
Use a program like mksquashfs or gensquashfs to create a suitable image.

Should the man page annotate mksquashfs and gensquashfs in any particular manner?

Yes, I really like that! I have no preference on order, but please use
.Sy utility
Or if possible
.Xr utility 8.

Are either of the generators ports?

Yes, both are in ports. It didn't sound like there was a standardized way to link to those, but perhaps I misunderstood.