Yes, hoarders do suffer from mental illness. If this person refuses to get help you might want to find a different place to live. I've seen people go into hoarding after a loved one dies, or because they are suffering from an illness like bipolar disorder and/or OCD.

feel sad for you, hoarding is bad - my 80yrold reli. is one - thats alot of hoarding stuff. To make matters worse the memory is going fast - dementia or mental health not sure - does it matter - but whilst reli. still enjoys relative independence it cant go on for much longer - house full to brim - literally, only someone such as yourself will understand the truth in that-and so much anger when you try to suggest a clear up...........Ive given in gracefully - all can be responsible for consequences of own actions - serenity prayer rules- and i recognise i cant change these behaviours for my reli.
Good luck x