I thought I'd mention that I've actually brought this subject up in a forum that caters to sex workers and their clients. I actually made a poll asking whether people thought there was crossover. Here's the results so far:
1- Yes, there is some crossover between all 3 categories: 12 / 40.00%
2- There is only crossover between sex work and swinging 5 / 16.67%
3- Sex work stands alone; there is no crossover. 13 / 43.33%
I decided that I should put a poll in this thread as well and have just done so for anyone interested in seeing the results/voting in it.
There has also been some discussion as well: