How realistic do you want to be?
We have nomadic people in the world today such as the Sámi of northern Norway, Sweden, Finland and Russia, and the Romani, who are sometimes known as Gypsies. But, while nomadic people were once a large demographic in the world (even creating empires), they inevitably diminish as knowledge makes stability more efficient.
Offhand I know of no nomadic minority that hasn't been treated as second-class by the dominant civilization(s). The nature of their society makes them untracable, untaxable, and very easy to blame for every crime imaginable — all of which makes them hated (or easy to hate). And they could be enslaved without anyone seeking redress.
Using humanity as the guide and generalizing something awful, the egalitarian society you're talking about can't practically exist without communication, record-keeping, and both legal and political representation. And despite having all that, we're having trouble working all the kinks in that out today. History has proven that, from the perspective of a society, it's difficult to give up the habit of hatred and dislike. Humanity evolved competitively, and we often find oursleves going back to our deepest roots, looking for "us" vs. "them."
Add to this a civilization with sufficient agricultural knowledge to allow stable fixed-location societies and we have very little reason to trade with the nomads. Cattle, horses, meat... All are a part of agriculture. Unless you're talking about artificially stagnating innovation, animal husbandry goes hand-in-hand with agriculture. So, the only value the nomads would really bring is as traveling merchants and they'd be supplanted by trade organizations (see the American West which started with both the indiginous populations and trappers both eventually giving way to expanding populations and transport technology).
So... viable?
No. And now you know why I'm not a fan of questions that ask if something is viable, feasible, possible, realistic, plausible, or anything similar. The only two references we have is Real Life where the answer is 99.9% of the time "no" and your imaginary world where the answer is 100% of the time "yes."
So, don't let this stop you from writing a good story.