Otter work with PowerShell DSC resources (i.e. a single configurable item).
On its own, Powershell DSC defines configuration as a graph of resources (similar to how Puppet works), and "DependsOn" is one of the mechanisms to construct that graph. The graph is nice, except it's totally unpredictable which order things run in, which is why we decided against the model in design.
Otter, on the other hand, is more procedural (like Chef, Ansible), so we cannot import a concept like "DependsOn".
To define your configuration in Otter, you instead use "roles"; we will soon add a feature called "role dependencies", but this will basically just automatically add roles at configuration time when needed.