The pioneers of "Pioneers! O Pioneers!" are rugged, sure. And they keep themselves apart from the comforts of civilization. But they are not loners, no sir. Their bond to each other, including pioneers past and yet to come, is one of their defining characteristics. Their unity is reinforced over and over, as our speaker describes them repeatedly as moving in a single group or formation.
Pioneers are so bonded because the west wasn't won by individuals—it was won by cooperation.
These pioneers are individuals. The speaker just chooses to gloss over that fact, because pioneering is a national endeavor, not a personal one.