If the airline requests to see a ticket out, simply explain that DTV holders are stamped in for 180 days and it's not necessary. Show your printed out Visa and direct their attention to the 5 year validity. Stand your ground.
Anonymous participant don't look at the requirements as they can request almost anything, look using the search tool in this group to see what others have stated about their experience at HCMC
Anonymous participant don't submit them initially, but if your research shows the particular embassy always requires it, then you're just delaying the inevitable. Absolutely a very brief cover letter helps
It's been done. You could include a brief cover letter stating family emergency that required unplanned travel to a different country before the dependants/spouse were able to apply.