Readers - Simple question complex answer. Nothing is usually simple in nature. There are usually numerous ifs, and it all depends.
The dark spot on the rear lobe or soft rays of the dorsal fin is quite variable and not a reliable physical character by itself for separating the BG, sunfishes and their hybrids. The dark spot is to be used in combination with more prevelant characters for helping to separate the sunfishes. Recognizing hybrid BG or hybrid sunfishes consistantly and accurately is pretty difficult due to the many combinations that could occur in natural populations. The ability to recognize hybrid sunfishes is as much art as it is science and the ability is learned from closely looking at literally hundreds or thousands of the various pure strain sunfishes from DIFFERENT habitats. From that one can have a good 'feeling' or learn to recognize more the obvious differences and the combination of various features from the parent speices that often show up on hybrids. This all becomes more difficult when the obvious physical features of hybrids are diluted (due to back crosses) from numerous generational spawnings that mask the hybrid genetics. Bottom line, don't rely soley on the dark spot on the soft lobe for much of anything when it comes to the sunfishes.