Linq to Sql gives you the ability to read data as well as Insert Update and Delete.

I looked through the source code unit tests and the docs, I only see mention of using Linq to LLBLGen to Fetch entity and entity collection data. I see no mention of how / if Linq to LLBLGen supports update, delete, insert.

Since I am using adapter, is it safe to assume that after I use Linq to fecth some entities/entity collections, that I should commit changes to those entities/entity collections using the standard adapter.DoXyzOnEntity or adapter.DoXyzOnEntityCollection methods?

Yes. Linq is a query tool, so you only ever fetch sets. You can then persist these fetched entities again using the normal channels. The difference with linq to sql is that we don't support lambda filters on delete/update.