When referring to the home equity line of credit, you are correct that RESPA does not apply if early disclosures are given correctly.
So, not having a copy of any HUD would not be a RESPA violation. And if RESPA is not applicable, I would not keep a copy of any HUD. You never know about some examiners and whether or not they will write you up for not really knowing when RESPA does/does not apply. Why take chances?