On the first part, nope, not that I've found...
if you elect to go directly to tape, you want to make sure you have enough
tape drives available when it starts...
This is why I like to go to a diskpool first (even though we are about to
roll out our first "direct to tape" environment)

On the BKI, it is just a warning...
        but if you are only using a single archive management class the data
will go to the same storage pool and thus stand a high probability of being
on the same piece of media, main reason to request two copies is to protect
against loss due to media failure.  If you are making two copies via backup
storage pool you don't need the TDP side to make two copies but if you are
using  backup storage pool to make the copy you still stand the chance of
finding out your media is bad when you go to make the copy.

If you have a  bad backup (archive) of a data base file you can go back to
an earlier copy of it and still bring it up to where you need if you have
the archive redo logs... if you don't have your archive redo logs, you can
go no further.
(that is why TDP allows for a push of multiple copies, with the intent of
going to different management classes and thus, hopefully, different pieces
of physical media)

later,
        Dwight