Requirement when submitting app to Apple
I have seen many apps do this and there is no documented requirement as to what the support URL contains.

Table 10-2 of the iTunes Connect Developer Guide (Editing and Updating App Information) contains the reference to need to provide a support URL and there isn't any mention of requirements. 

Clearly, the reviewer may visit your site during the review process and perhaps have a software monitor it periodically. 

I've not known them to send a request for support during the review process, but I'd hate to fail review due to this item.

My advice is to be absolutely clear and indicate where on your blog the support avenue lies. I'd also set up third party monitoring of that URL in case it goes down during review and once your app is live on the app store.