I just received my SM3's a few days ago, and I don't find them veiled as such - even though they are far from being as transparent as my HiFiMan HE-6.
I do however find the SM3 a little "veiled" in the first of the below two general types of veil (when talking about a headphone or loudspeaker) that I describe below:
The first type is caused by excess bass and lower mids, and the "veil" is in other words gone or lessened considerably when you equalise this away. This is a common experience when you put a loudspeaker too close to the wall behind it (this boosts the bass), and it disappears when you pull the speaker away from the wall. In terms of universal iem's a misfit might produce a smilar effect. In other words this is a subjective "veil", that is caused by too much of some frequencies, and not due to bad driver quality. This kind of "veil" is (theoretically) seen in a frequency response chart (which shows the quantity of the different frequencies).
The second type is veiled as opposed to transparent ("a real veil"): This is due to low(er) quality of the driver(s). When I say quality here I mean the ability of the driver to respond precisely to the electrical audio signal it receives. This is f.i. shown in square "wave" response charts and shows the speed of driver (how fast it starts and stops). It is also shown in the amount of harmonic distortion the driver produces. This type of veil is heard as if there is a thin curtain between you and the music. This "real" veil is best heard on quality recordings and using quality audio gear.