The Wiki link for the series says that some of these cameos were done as uncredited, unpaid walk-ons. How, if any, would this complicate the rights issues?
It wouldn't. If they weren't credited or paid appearances in the first place, the performers in question couldn't get any residuals, ever. An extra cut of nothing is still nothing. And as stated, even most performers back then who were
credited and paid didn't get residuals specified in their contracts.