More than likely they would still work. I have 10.5.4 Server installed on my laptop and can still access the ReadOnly account. Though with any upgrade it's probably best to start with an upgrade to a non-Production environment and then you could verify that your custom admin views are still working.
As per my understanding.
With the upgrades you might have additional tables getting added to backend DB etc but that should not impact the READ ONLY ACCESS
to custom views.
As suggested first try your hands with Dev env
Generally speaking, when you're applying patches, there's not any structural changes applied to the underlying tables or the addition of new tables. It's not 100% certain, but mostly. We have custom views, and they continue to work from 9.3.x to 10.5.x with the readonly account.