Not immune, but certainly not as bothered by them as some genera, as per Candace's post (which I hadn't read before I responded!)
They are more or less. One thing, most hobbyists and professionnals get their orchids tested for 2 major viruses, CyMV and ORSV, and sometimes BYMV for masdevallias, plus one or two others ( Tomato Ringspot, etc...)
I visited the cloning labs of some companies. Back to several years ago, those labs were generalistic, from orchids to tomato, to micrografted zucchinis. They did not care at all about cleanliness of the tools, they were there to make very, very cheap "plants.
At the same times sprouted the first reports of tomato ringspot virus and some others in orchids. The dreadful Orchid Fleck Virus ( apparently seed transmitted as well), and many others attack any type of orchid, anytime.
Some nurseries used their breeding plants as cut flowers when they did not want to exhaust the plant. Hence, they cutted the flower stems... Some others got a worker cutting a couple brown tips on the plants when they repot, etc...
Basically, I got virused paphs, tested for CyMV and ORSV, but I suspect that some chlorosis and necrotic patches can be virus-induced. I have no proof for that, but it is possible. At any rate, I have seen sometimes seedlings a couple of months out of flasks with very heavy necrotic and chlorotic patches, that did not test for any known fungus or bacteria. Apparently the others grexes were not affected in this dutch nursery, so it should not be a mineral deficiency. Remains only virus, or nearly so, as a possible cause. BYMV in paphs is most frequent, to my experience, in old complex hybrids and some pot plant types, but there are so many virus that it is impossible to assume a plant is really virus free, except by complete ELISA testing ( we speak about a thousand or more US$ for all the viruses known, only for the reagents, not the workers !), followed by electron microscopy.
As well, before many people were sowing paphs as dry seeds. Now, to gain time, most labs will do green seed caps, so virus transmission is likely... I had sometimes flasks from a few suppliers whose seedlings would never perform well, and always have kind of chlorosis and necrosis at a time or another...