Oh I absolutely don't think it should be housing + no rehab. It's just housing first. Having people in a stable location makes it much easier to connect them with services like substance abuse treatment, mental health treatment, job training & placement, etc.

Here's one study that looked into it:
https://pubmed.ncbi.nlm.nih.gov/10737824/
Conclusion: "The program's housing retention rate over a five-year period challenges many widely held clinical assumptions about the relationship between the symptoms and the functional ability of an individual. Clients with severe psychiatric disabilities and addictions are capable of obtaining and maintaining independent housing when provided with the opportunity and necessary supports."

Here's another, this time with more mixed results:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1448313/

"Participants in the Housing First program were able to obtain and maintain independent housing without compromising psychiatric or substance abuse symptoms."

People were more likely to remain stably housed with a housing first approach.

The most interesting highlight for me is that the housing first group had lower levels of engagement in substance abuse treatment, but basically the same levels of actual substance use. This shows that forcing people into substance abuse treatment in order to receive housing is ineffective.