From my limited understanding, over the years Old Believers were simply left alone, thought of as kind of weird by some, respected by others for their piety. Somewhat similar to how many Americans view Amish: quaint, a bit odd, but obviously religious. My own Russian family members look upon these people as just very devout and serious about their faith, and that they *live* their faith.
I'm not totally sure about how they were dealt with during the Soviet era. One thing that always bugs me is how many people in Western countries have this huge belief in the "Iron Curtain" and people having to read Bibles in their basements using flashlights. Not so, unless you're talking about *protestant* faiths. Russian Orthodoxy was not encouraged (atheism was) but it *was* very much tolerated, at least in some parts of the country. Therefore, the "ultra Orthodox" (Old Believers) probably were not bothered too much. After all, it was the Soviet Union that encouraged the culture, language and beliefs of various ethnicities, perhaps Old Believers were included in this. But again, I am not 100 percent sure about this.