Sorry to ask but ... are you sure that you really want / must do that?
Why would you join 2 tables with nothing in common? What kind of result do you expect?
You can always do a nice cartesian product: 1=1, it just make no sense but ... why not ....
So try to maybe explain a bit more your context and what are you trying to achieve, in that way you get a better answer ...
PS: in OBIEE when querying 2 dimensions tables there will always be a fact table in between, an implicit fact table. So if you want to avoid that implicit fact table you are not joining 2 dimension tables but one of the 2 must act as a fact ... and here you see why what you ask is a bit strange ...
+1 on Gianni Ceresa's input: Why?! If there's no relationship between them then why join them? What's the use case and the point of it?
Taking the usual - wrong - use case of "oh it's to export it to Excel" then just UNION ALL it and be done with it. Doesn't make it right but at least doesn't pollute your models.