Unfortunately you cannot enforce that Creator and Requestor are different for ticket workflow approval steps. The (Ticket Requestor) can be used to dynamically retrieve this information from the ticket, or a default approver can be supplied. You are unable to conditionally switch between these two depending on the Ticket Creator.
In addition, there is no way to filter report data by comparing values from multiple columns. However, you can select both the Created By and Requestor fields for a Ticket Report. Additionally, these can be placed next to one another by clicking and dragging on the Sort icon to the left.
You can then click the Add button in the Order your Report section and order the returned results by Requestor and/or Created By. However, this would still require that you look through each row in the report and find the duplicates.
If you find that too many results are being returned in the ticket search, you could limit the search to specific user groups. This can be done by adding Created By and Requestor to the filtering section, and selecting is a member of operators for both fields.
You can then provide the same user group to both filters to ensure that the Creator and Requestor are in the same group (although maybe not the same person). However, this approach will require you to run the report for each user group in question, and you will have to update both filters before re-running the report on a different group.
I hope this helps to explain the limitations with comparing Creator and Requestor for ticket workflows, as well as how you can report on this information. Please let us know if there is anything else we can do for you.