The FieroRust picture is the one that would make me most nervous about the
car.  there appear to be a couple rust holes all the way through the frame.
Yes, that is the engine cradle.

It is hard to tell from the others.  They could be surface or all the way
through.  Your mechanic is probably better suited to giving the final answer
than anyone who is just looking at pictures.  He would know if it is
possible to clean up the problem areas and weld in appropriate bracing to
bring it back.

In case you don't already know, your next problem is that you have an 88.
There are a lot fewer of them out there and the engine cradle is nothing
like the other years.

One of the ears holding on the right forward lateral links broke on my
Formula this year.  Fortunately, I had a spare engine cradle from my
previous Formula.

You might want to contact Ed Parks at the Fiero Factory
(www.thefierofactory.com/).  He has many salvaged Fieros and parts for them.