I can come up with reasons why and why not. Heroku is a Salesforce owned company that does have some integration with Salesforce, but it is still a separate platform.
I guess it depends. If the questions are integration with Salesforce related questions like the one recently posted on Overcoming Database.com latency on Heroku then I think they are totally appropriate. If the question has nothing to do with Salesforce, for example, something like "How do I get my config file set up correctly", I'd say that doesn't belong. That type of question is on par with asking a question like "How do I set up the applicationContext file in my Java Spring web app" and is not directly related to Salesforce.
For me, the key is that the question must contain some sort of integration with Salesforce.
Heroku is a Salesforce product and is part of App Cloud. Any product-related question about Heroku is welcome here. Programming specific questions that are unrelated to Heroku should be asked on Stack Overflow.