Integrating Visio with SharePoint

I am working on integrating Visio web parts (data from SCOM) with SharePoint 2010. I followed technet documentation and finally get it working. What I want is to understand under what account "Service Application Pool – SharePoint Web Services Default" should actually works? The default is local network service account

Here is http://technet.microsoft.com/en-us/library/hh920810.aspx a description that this account (Default network service) should be then configured with Operations Manager Read-Only Operators – User Role. I did it by creating AD security group and then add sharepoint computer account into this group as it is not possible to add it straight to Operations Manager Read-Only Operators – User Role. 

I am using also Secure Store Service and application id in Visio Graphics Service Settings

So the question is under what account "Service Application Pool – SharePoint Web Services Default" should actually works? As a best practice 

And next question what account should be set for Target application used for Visio Graphics Services ?