Can't comment specifically on the vinyl, as I'm presently digital-only, but I've used the A-D coverter in the Tact with SACD (analog out) and it definitely was missing some of the expected magic that SACD can provide, when compared to the CD layer going digital direct.
Room correction was applied in both instances. However, comparing CD in bypass (without room correction) to SACD with RC, I preferred the SACD. Since I don't have an analog preamp/amp I couldn't compare the SACD with and without the A-D converter, though.
When I use the A-D from my HT preamp with Satellite music or movies, it sounds pretty good and I don't seem to be missing much. Expectations here are different, though.
So...I suppose the losses are minor but real, and I think whether or not the detriments outweigh the benefits will likely depend on how bad your room is--and therefore how much you gain with room correction vs. the losses in the A-D converter--and whether you plan to listen to vinyl significantly more than CD.
Here's what KR had to say in Stereophile about the A-D in the (previous generation) Tact 2.0:
"An FM or vinyl signal passed through the TacT with room correction bypassed sounded quite good, but there was a consistent and small loss of detail, along with an overall brighter sound, than when I fed those sources directly into the Line-3....Overall, the influence of the TacT's ADC was greater than and swamped the differences among the DACs. Nonetheless, it was not so obtrusive as to prevent the TacT from being used effectively for room correction with analog sources."
From what I've heard from others, the newer A-Ds are significantly improved, though.