My question is similar to this question but in my case I am wondering can two of the SAME version of TFS (2013) share a data layer. I cannot find any documentation stating that it is ok or, alternatively, that it will cause issues.
I am wondering if this would be a viable option for testing setting up a new instance of the server but I do not know what issues having two TFS instances connected to the same data layer / database may cause (or if its even possible).
The immediate answer to your question is, "Yes". However, it's not what you want. You can configure multiple application tiers pointing to the same database; that's how you enable high availability/failover scenarios.
For testing purposes, you should create a second set of infrastructure.