Can an Inferior Infiltration trooper deploy in enemy Deployment Zone? And if no - then why is the wording different from Level 1?
No he cant. Read red "Important" box difference between Infiltration & Inferior Infiltration: infiltrator MAY deploy on enemy half of the table, Inferior Infiltrator MUST try to deploy on enemy half.
What happens if they fail the Infiltration roll? Do they deploy in your DZ or are they considered lost?
Deploy in your DZ in contact with a board edge, losing their marker state (if they had one) the same as other levels of Infiltration.