Assuming your manuscript was uploaded within three months of acceptance and/or publication, yes, your publication is still REF-eligible.
The Open Access Team regularly checks the metadata, files, licences and embargoes of items held in Apollo. However, as some items are deposited before publication we cannot know the exact embargo end date, so we need to update this once publication occurs. That means that some items in Apollo will have incorrect embargo dates (e.g. 2100-01-01).
No REF output will be invalidated by having the wrong embargo.