I have never use a custom action for Nenu. The out of the box Nenu action library is more than what I need. I don't see a reason why not. Test out the custom action in dstudio but find dStudtio is very forgiving. A real test would be with dcDesktop to see if the action will work. Essentially creating a nenu apps and run it for testing. Call your custom dll and test. Perhaps play with one batch to see if the custom nenu action works.
Nenu is to clean up the relational DB. Here is a link that impact Datacap performance as a hole if it's too big. If you can reduce these table, it will keep the DB nice a clean for optimization.
https://www.ibm.com/support/pages/db-tuning-recommendation-and-best-practice-datacap-enterprise-setup-0
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