I've seen a fair number of those on LA engines over the years. In my experience as well it always looked like the cam lobe was ok.
I had never chanced it and always replaced the cam and lifters, figuring another one was probably not far behind. In each case once the cam was out, it was pretty apparent the lobe was starting to go flat, even though it sure didn't look that way viewed through the valley.
It sounds like you were wondering if a valve stuck open would cause this. I don't think so. Chances are the lifter just wore through the hardness and starting cupping. If the valve was stuck closed I'd guess you'd see a bent pushrod. I've had that happen on LA's and even slant sixes that had sat for a long time.
Anymore before I try and turn over one that's been dormant a long time I will pull the valve covers and rap on each valve stem with a fiber mallet just to be safe. Some may say that's asking for trouble too, but I've found a freed up more than one stuck valve that way.
Lead, follow or get the hell out of the way