The hidden album has a flat structure. But you can create a structured Hidden album with smart albums and albums.
Any smart album with the rule "Photo is hidden" will show the hidden photos matching the constraints of the smart album, even if the Hidden Album is hidden. I cannot test this for the system version given in your signature "macOS 10.13".
But on macOS 10.14 Mojave or newer the following is working well for me. For example, in Photos 6 on Mojave I am adding all photos I am planning to hide to an album. For example, the original versions of edited photos or alternate edits are hidden in an album "Originals saved", or other albums are containing the photos sent to me by friends and family.
Once the photos have been added to these albums, I am hiding the photos.
For the albums, where I want to be able to see the hidden photos I am creating an accompanying smart album, like this:
This smart album is showing all hidden photos from the "OriginalsSaved" album, even if I have hidden the Hidden Album with the command "View > Hide Hidden Photo Album".
Or, to see all Hidden photos from a certain date range we can use a "Date Captured is in the range ..." rule or tag the photos with keywords and use a keyword rule.
I am keeping such an album for each person who is regularly sending me photos. These custom Hidden albums are collected in a subfolder, where I can quickly find them. And photos which I want to keep out of sight can be excluded from all smart albums, by taking care that the constraints do not include them. Use a keyword "never_show" or similar and add a constraint "keyword does not include "never_show".