We do not have SIM implemented either but we had Ariba add 4 custom fields in the Organization Profile section of Sourcing which we use to identify divers suppliers.
You should be able to have custom fields added to your system as well. Just make sure that you tell Ariba that you want the fields to be reportable or you will not be able to pull them into reports. I believe it you make them mandatory the next time someone form that company loges into your Ariba site they will have to answer the questions so you should be able to get your info quickly.
Once you have the date fields reporting is easy.
Which version of Ariba are you on? Are you an On Demand customer?
Yes, we are an On-demand for Sourcing
If you are about to implement SIM, then this should make it easier for you.
Your first problem will be to collect all the diversity information into the supplier profile. You can do this by pulling all the supplier diversity quesitons into a RFI (linked via the Sourcing Library) and then inviting all your suppliers. Since you pulled/linked all the questions directly from the supplier profile, when a supplier responds to the RFI, they will automatically populate the supplier profile for you. Don't forget to include other quesitons (outside of diversity) that you may want to track about your suppliers so that you collect this information once.
Once you have all this data populated, then you can create an analytical report and use the diversity indicators from the profile when building the report to see which suppliers have participated in a RFx or which you have awarded to.