Not as "vendors" per se, but as members, like any individuals? Sure! They are welcome to support their customer base on this forum, as it helps disseminate information, and everyone benefits. Although vendors cannot advertise their products, this builds a good reputation for them on this forum, and indirectly encourages members to consider purchasing products & services from them. Our endeavor on this forum is to be vendor-neutral, to provide the membership a means to reach an informed decision.
Please also remember to show your appreciation for your vendors when they have done well by you (in the feedback area), and be supportive of those who choose to go a different route. Diversity is a good thing.
/end soapbox