Hi,
Technically speaking, since the dashlets aren't embedded in any kind of Iframe, they share the same context. So they should be able to interact (create a specific ID or classname in some element on dashletB and document.getElementById can easily retrieve it from dashletA)
However, conceptually, dashlets are meant to be independent entities and should be self-sufficient and not impacted by the outside.
So, what is your use case?
Couldn't you just create one single dashlet composed of 2 sections (potentially tabs) that switch after a link click?