Have you noticed how bokeh tests often have some portraits shot outdoors with foliage in the background?
Because I've been making a list of my favorite portrait photographers and portraits, and there is almost never any foliage in the background.
Do you know any great photographers who like to put their subjects in front of backlit foliage?
By 'great photographers' I interpret you mean famous and/or highly regarded in the history of photography.
Off hand, I can't think of any.
Shooting (often wide open) backlit against foliage is something done quite a lot in contemporary wedding photography. While perhaps few, if any, of these photographers, including myself, would be deemed 'great' in respect to contribution to the history of and continuation of the art of photography, IMO it doesn't matter.
What matters is clients' reception of the photographs, usually of themselves. If they look good and appear in interpretations different from what they are used to seeing (from smartphone selfies), they'll be happy. Given the influence of social media on current perceptions, many have probably seen 'foliage bokeh' photography throughout various media streams, and have probably liked it.
Tying in the debate here about what is and isn't professional, IMO, fulfilling clients' wishes (while injecting one's own 'creativity') is ultimately the point of being a professional photographer. Whether strobe-lit or available light.
On this last point, it certainly is possible to do pleasing work with available light, but often photographers, especially professionals, are under multiple constraints, whether time, location, season, weather, etc., etc. Artificial light is a solution that returns a considerable degree of control to photographers working towards clients' wishes (of making them look good).
