How can I identify if my device is using ART runtime or a Dalvik?
Short answer: unless you've changed it yourself, it's Dalvik.

Dalvik is currently the supported VM for Android. ART is a new VM, which is expected to become the supported one for the future L release. If you are using the L developer preview, you're using ART.

In KitKat, there is a preview (an early beta version) of ART, which you can turn on from the developer options. It's not recommended to do this, because the preview has bugs and is not yet compatible with all apps. The option's there primarily for app developers to test their apps with ART and report bugs.

So unless you're using the L developer preview, or have turned on ART in the developer settings, you're using Dalvik, which is the only recommended option for end users.