At this time you are unable to create custom reports for Project Request Resources. When a Projects and Requests Report is created through the Analysis application, you are able to select the Resources column. However, this column only returns users and NOT functional roles.
Thus, even if you add a filter for Item Type = "Request", the Resources column would be blank for this. The purpose of the Resources component of a project request is so that a functional role can be selected and another individual can staff the project with users who suit the use cases of the associated functional roles. In terms of reporting however, all custom reports will only return resource information at the user-level instead of the role-level.
In the Resource Management application there are a number of canned reports that may help you report on resources. The Resource Requests > Requests Search report allows you to filter on specific requested functional roles and/or projects. In addition, this application has the Reports > Projects By Resource Report, which allows you to report on similar data.
I hope this helps explain why you are unable to view Resource information for custom Project Request reports, and provides information as to how you can view relevant information. If you find that none of these reporting tools provide you with what you need, I can create an enhancement request on your behalf. Please let us know if you would like further clarification or there is anything else we can do for you.