We tried the same but without success. Anywhere in the community I read something that the SurveyMetrics Business Object would ignore created business rules. This is exactly what we figured out.
When I looked in to this a while back the Survey objects are not true Service Manager Objects, it was not possible to run business rules or triggers against these. The classic example most customers were asking for was if a rates of <3 then generate an alert. It might be possible to do this using analytic metrics but I have not got round to playing with it.
If you need this functionality please raise it with support so the request can be added to the RM or a new RM raised.
This is pure theory, as previous posters said, the Surveys do not work with business rules or workflows, but! every time someone answers a survey the responses get linked to the Service Request / Incident, so probably a Business Rule inside the Service Request to run when it gets linked to a "Survey Result" would work:
As you can see, there are few Service Request - Survey relationships, you might have to try playing around a bit, I would start using "SurveySession" as the "SurveyResults" most likely it will trigger for every individual response (But if "SurveySession" does not work and "SurveyResults" sends too many emails, you can always use a flag "SurveyNotificationSent" and turn it to true the first time, preventing the rest to trigger...).
Again, this is pure theory, but I fail to see why it would not work, it is not very powerful, as filtering per results (i.e. sending the email only when the surveys is under 3*) is not going to be easy (most likely not possible at all), but if you want to send the email for every survey, it might work.
If you try it, let us know if it works... I can see my manager asking for this in no too long