Personality (negative personality traits) isn't considered a disability, it's considered a lifestyle choice. IE the person could change if they wanted to, if their way of behaving wasn't working out well for them.
People with a diagnosed personality disorder may also be considered disabled. It would depend on how it affected them and the effects that had on their everyday life. People with a personality disorder can sometimes meet the criteria for successfully claiming PIP.
Not being able to get through ordinary daily life or life going wrong in some way such as being unable to hold a job or becoming homeless or an addict etc are things that may drive a person to seek help for their MH, which may then result in a PD diagnosis.
I would also say this person would be better off living somewhere self-contained. It can be stressful living with a random group of other people. I’d be wondering why the support worker wants to place them in a house share not a bedsit.
They probably can't afford a self contained place. Though I agree it would be better for them if they are ND. The need/desire to constantly mask (although in this instance perhaps not very effectively) around others, even when at home, isn't great for someone's MH.
The HMO with a LL renting out a room to each tenant with no consideration to existing tenants is a little different to OP running a house-share. The tenants in a house share will have more to do with each other. They'll be jointly liable for all the rent, utility bills and council tax split between them, a joint tenancy agreement naming them all. It's a lot more personal than living in a HMO and it's normal in a house-share to find someone who fits in with the rest so everyone is happy. In terms of this, probably vulnerable (since they claim PIP so are officially disabled and have a support worker) person, living in a house-share with ordinary quiet sane sensible people is likely to work out better for them than living in a random HMO filled with whoever, where they may end up beig bullied or harassed by the other tenants. Unfortunately throwing someone who is really in no fit state to house-share into that mix is going to detract from the other housemates quality of life.
The housing support officer rally needs to find your applicant an assisted living place…ideally on a ground floor!
With this person being capable enough to show up to a house viewing, alone and have a conversation about the rental with the LL, I'd say they've got precisely zero chance of getting placed in an assisted living facility.
The problem for OP with all those posters saying just tell the support worker about the harassment, is twofold. First, the support worker isn't averse to a bit of harassment herself so is less likely to view her clients behaviour as a problem. Second, all it would take is for the support worker to announce that this excessive contact from her client is as a direct result of their disability causing them to behave that way and decide to take it further, for OP to end up in the very situation she's worried about of being accused of disability discrimination. If this behaviour is being driven by disability, OP may well have no grounds to refuse the tenancy due to it, regardless of her resources to cope with it or not. This is why it's better to say nothing at all. At the moment OP doesn't know what this person's disability is or how it affects them so can argue she hasn't been intentionally discriminatory. If the client and their support worker gets no further information from OP, they'll be hard pressed to argue any disability discrimination has taken place.