Okay. Thanks for the terms Tromboniator, but still it has not solve my problem. In the mentioned example I put there, I can select the hidden (any terms), while in another document I cannot.
I just figured out that I had some locked guides in my project that were preventing me from selecting all objects in my layer. Once I unlocked the guides (from the menu: View- Guides- Unlock Guides) then I could select everything in my layer, including hidden objects. This may not fix your issue with getting hidden sublayers to select, but it's something to check into.