Views 3, 2 different node types, filtered by the same contextual filter
If field_nodea_taxonomy and field_nodeb_taxonomy use the same taxonomy vocabulary, this problem can be addressed differently with a shared field.

I generally define a single shared field for each taxonomy vocabulary, and use it in every content type where it's needed (e.g., nodea and nodeb). If your requirements permit you to use this approach, your problem goes away, since a term filter on that single field will work for all content types.