Why not? Wouldn't any group want to have a Super Mutant with Dual Miniguns and some torn off Power Armor slapped over his shoulder or his knee? Wouldn't they enjoy having a Ghoul to send into High-Radiation areas to get weaponry for them? They could even have ferals on chains outside their settlements.

You're thinking too small man...

Pirate ghoul with cybernetic peg-leg with ninja training riding a laser raptor.

I got chills. You truly are a gem of our generation.

I chalk it up to Raiders preferring not to get eaten.

"Go get that feral."
"YOU go get that feral..."
"Let Jimmy get the feral."
"Jimmy died when one of you idiots thought a Super Mutant would be interested in signing on."

I mean, the Super Mutant could easily be a "warlord" type. There could even be full on Super Mutant raiding groups. It's common knowledge that Super Mutants and Feral Ghouls normally get along without conflict, so the Muties have Feral guard dogs as a first line of defense. Maybe even an armored Glowing One because everyone knows that Super Mutants and Ghouls like and are even healed by radiation. Having a few Glowing Ones in the group would mean regular healing and actually implement some strategy and require the PC to pick and choose his targets more carefully.

And here I thought all Supemutant parties met in the wild were raiding bands. Seemed like what they did in Fallout 3.

Well thats fantastical racism for ya, plus groups of that nature usually forms once then never really recruit, they tend to develop aggresive "we vs them" mentalities.

Considering I can count the number of Vault 87 Strain Super Mutants willing to converse on one hand, most seem content to follow their conditioning to continue dragging people to toss into leaky vars of FEV. Not work with outside groups for survival.

These aren't Mojave super mutants. Dumb as bricks and meaner than Gordon Ramsey after being handed burnt toast.

He-Who-Remains:1
Robotoh: 0

I think it would work for Super Mutants, sure. I'm not too keen on Ghouls since they tend to be like outcasts and frowned up. They're still human under that salami skin. Super Mutants have raided Vaults to turn humans into Super Mutants during The Unity, which was over 100 years or so. However, there are hardly any FEV vats to create more Super Mutants, especially on the east coast, so it may affect the lore a bit. Still, I'd love Super Mutant raiders attacking my settlements with their little Centaurs.

kanye west?

I don't think super mutants would ever join up with humans like that. For the most part, regular humans hate super mutants. Ghouls make more sense. They're obviously not all good people, and they do bring some advantages to the table.

Take a look at http://fallout.wikia.com/wiki/Broken_Hills. They weren't raiders but what you said is not entirely true.

That's why I said, "for the most part". Broken Hills was a community formed around the protection of Jacob and Marcus and a mutually beneficial relationship between rad-resistent ghoul and super mutant miners and human traders. I don't think Super Mutants would ever join up with raiders, because if they wanted to, they're already quite good at taking out helpless wasters.