I think he's referring to the coolant side. Many heads crack like that but never leak water. Like Dwayne said, if it doesn't leak, cut the seats and run it.
The magnum era small block heads were bad for this.

In my experience, pressure checking a cast iron head will only show a leak if the crack is pretty bad. I have pressure checked cast iron heads that didn't leak when checked, but did leak when they got hot when running. Just saying if you weren't having any leaking issues when they were ran last, and they check good, then run em.

Putting a seat in it would be good only if the relief cut for the seat cut out all of the original crack.