Agree with RD. Heros species are widely distributed in varied water conditions, they're not from a single location and not always blackwater. For example, note this
fishbase entry for pH, hardness, and temperature range for Heros efasciatus, a widely distributed species. Captive bred types have been raised and adapted to a range of freshwater conditions-- within reason, of course. I've kept Heros since the mid 1990s, including some wilds, most of them in pH in the 7s and moderate hardness, as have many others. I've had some live 17 years, so most do just fine in those conditions.
Most yellow labs by far are captive bred and adapted to pH just about anywhere in the 7s. So, excepting a few blackwater Heros that aren't as adaptable (Heros inirida, for example), water is not the issue. Moderate pH and hardness can suit either of them, all the more so with common captive bred severums.
The issue IS temperament. I understand the temptation to keep yellow labs with various fish they shouldn't be with, because of their color, but I wouldn't keep frequently nippy, comparatively boisterous, and potentially aggressive mbuna of any type, including yellow labs, with calmer, slower, severums. Aggressiveness is a sliding scale. Yellow labs tend to be 'peaceful' only relative to other sufficiently aggressive fish, with the wrong fish they can be a pain ime.