They have and do.
But you still haven't answered the question. Should no Muslim do business or be employed at ports, airports, water facilities, borders, or whatever other facility someone may consider to be sensitive?
This may sound a bit arbitrary but no, I don't want Muslims with their often repeated hatred for us not to mention inability to control the terrorists within their countries running anything even remotely related to national security in this one. If they want to buy some Pizza Hut franchise I suppose that's different but ports no way.