I have noticed on some forums that it seems JV brokers are also Copywriters.

Is this a common thing or a trend for diversification?

Aaron

Depends if you position yourself as a copywriter or more of a marketing consultant. As the latter you will have many more opportunities to bring people together and take your cut.

Though I don't see many people marketing themselves as such, it just tends to happen when you're working with a number of businesses in similar niches...

I would say if you're a copywriter then be a copywriter. If you have to broker joint-ventures along the way then someone isn't marketing their copywriting business hard enough.