I think we should be encouraging vendors to participate on the site as much as possible. The major caveat is that it has to be an actual answer like you would expect from anyone else. For example it should not:
- Just tell them to contact support (unless maybe it gets to the point of being a bug, in which case they should include the resolution later)
- Be non-technical, this is a technical site. This means no marketing
It should:
- Be a direct and technical answer to the question
- Come from a developer or high tier support usually
On the vendors side, if they do it right, in my opinion it is better than any advertising they could possibly buy from Stack Exchange. Seeing the engineers behind a product reach out beyond their normal support methods says to me that the company is passionate about making something awesome and would put them at the top of my list if I ever need a solution that they offer.