The Hybrid PM / BA

BA is the foundation to start a project so if all seems good in BA then PM will follow and then through out the project you can perform business analysis to see that the profit of the project is heading in the right direction so I would say it is possible and good practice to do both.

Wait until Sergio see this question. I am sure he will have a strong opinion on this :D

My opinion: Hybrid might work for small projects but I do not think any can take the role of the other on large projects.

Do you mean act as the full time PM and BA on a project? If so, I'd have to advise against it. I was a BA before I became a PM, and while being a BA is helpful in my current position, it's VERY difficult to perform both roles because each consumes a lot of time and attention.
That said, you might be able to assume both roles on small, relatively simple projects, but doing so on a major endeavor almost guarantees you will become overstretched, and either your work or your personal life (probably both) will suffer.