Deleting a cache is irreversible. Do not delete the cache unless you're sure that you don't want to use a previous version of your project. This will not affect saved projects that already have elements in place.
Maybe you should describe what you mean by hidden elements!
The cache in Bridge pertains to thumbnails and other sizes of temporary images that Bridge generates and uses internally to quickly display each file in a directory. Deleting or refreshing Bridge's cache does not change the contents of the files being displayed, and hence represented by the cache, only their previews.
If u are still hesitant, just do an experiment yourself. It will only take u a minute or 2 to confirm this.
The cache in PS is for somewhat different purposes than the cache in Bridge, eg temporarily saving history states, etc. You can be confident of what Sam stated when u realize that PS's cache is cleared every time you close a file that u have been working on.