Am I reading this wrong? To me Contains can mean a connection vs Depends On which is more substantial.
Also, in my research I cam across a link that advised incidents can be created based on relationships, is this true?
Response from support if anyone is interested:
From the description, I understand you would like more details about service relationships, right?
Information
So, the service relationships are just for visibility, there's no aggregated feature in incident management when you have them. For example, if you create an incident for a service with other related services, OpsGenie will not create incidents for them.
The idea is to help you identify the dependent services (on the service's page) when you have an open incident with a service.
Regarding the error you saw, it happened because the "Contains" is like an umbrella. One service cannot be under multiple services but under only one. On the other hand, "Depends on" is like a link between two services. A service can be linked to multiple services.
there's a definition for them:
A relationship can be set up between a minimum of 2 services, up to 20 services for each relationship type. They can be a dependency between services (Service A - Service 
or containment of services (Service A = Service B + Service C)
