Well, the dreamhost wiki is (I believe) a customer-maintained collaborative enterprise, and it is very good and useful, but it is not the place to go to for questions like this.
Also, I am not looking for guarantees, I think they are basically meaningless.
What I am looking for is a statement from Dreamhost something like the following
(this is just a for-example)
The word 'usually' is deliberately vague, and that's fine. What we need, in order to make informed decisions about balancing risks, is good information about what a host is trying to do, and what its general track record of success is.
We don't (I think) have either of those pieces of information, with regard to Dreamhost.
We get customers saying "Dreamhost backed up my site with month-and-a-half-old data", and nobody clarifies whether this is exceptional, or normal.