in John Tullock's book, Natural Reef Aquariums, he has a picture of a mandarin covered with ich!!
resistant does not mean immune.
mandarins, dragonets in general, are supposed to be less inclined to contracting these parasites due to the aforementioned slime coat.
as with anything though, what you choose to do depends on your risk tolerance. as other posters have noted, having them survive a QT period in bare tanks is pretty much a no go. the argument could be made that you could try feeding them multiple times a day, but there are some big assumptions being made there. the first being that the mandarin will take the food you offer, the second being that it would be enough to sustain them.
my preferred method of QT for dragonets is a fully cycled tank with live rock. in my rig this is my grow out system. any dragonets, and some other difficult to feed fish like Rainford's Gobies etc..., skip the normal tank transfer process and go directly to grow out. here there is enough rock and substrate for them to graze on while i do a lengthy observation period.
now when i didn't have this grow out system up, i rolled the dice on my first mandy and placed her directly in to the main tank. this was the only fish i've done with this, luckily it worked out. as always, your mileage may vary.
so tldr; due to the complications with their feeding requirements, and their physiology (specifically the need to constantly be eating as opposed to one or two large meals during the day), i feel the best solution for my set up is to bypass my typical QT procedures. again, your mileage may vary, so please decide what works best for your set up, and know that either way there is risk involved. it is my personal belief that there is less risk doing some form of bypass to the "normal" QT regimen, than the risk to the mandarin trying to keep it alive during a standard QT protocol.
