I think a lot of it depends on you location, and the age of the body of water/course. Golf course architecture was my fathers greatest passion, and I grew up around quite a few golf course renovations/constructions.
Water hazards are very difficult to remove, but they are often added and re-modeled. As a result you will likely encounter a lot of bodies that have zero fish in them. As a little kid I would often ask if there were fish in the water, and either a greens chair, greenskeeper, or my dad would usually say no. Additionally, I know that there are very few fish on the surrounding courses is my area. On my home course there is a fairly big pond and its either natural, or built before the 20th century. The only thing over an inch in that hole are giant koi that were stocked in there 20 years ago when they renovated the course.
long story short, if you're going to fish on a golf course, the first thing you should look for is a pond that is very old and natural. Its highly unlikely that the water hazards are untouched eco systems, and even more unlikely that they are stocked. Now, its highly likely that this varies by region, as I wouldn't be surprised to see somebody flip into a hazard on a florida course and pull out a peacock that was introduced for conservation issues.
most of all stay legal!!!! most of the courses near me have night rangers at the least. Im sure some have law enforcement that patrol occasionally. The last thing you want to do is get trespassing+ charges for enjoying yourself. You never know how kindly the members or administration take to others. if you can, speak to the ranger beforehand, or talk to the greenskeeper during the day. many of them live on course property and probably would be glad to give you the green light for the occasional 6 pack on their porch.