The real question is, are the upvotes actually blind? You say that someone went and upvoted every post in a tag, which is definitely suspicious, but are any or all of those votes unwarranted?
In other words, how sure are you that you're dealing with blind voting rather than someone with expertise in [tag] who actually determines that these are all good and useful questions and answers? As yannis mentions in comments, it's really not all that unusual to load and read a lot of posts in a row, then go back and vote on them all at once.
(On a side note, I also noticed this recent Literature Meta post. I have seen regular users on Islam.SE (where I moderate) take similar such posts as an encouragement to seek out and upvote posts that they feel deserve recognition, often heavily and often for days at a time; naturally such upvotes would concentrate under the tags that they are particularly involved in.)
The main thing I would look for is posts that probably shouldn't have been upvoted receiving upvotes. Presuming that you as a moderator don't have particular expertise in [tag], you can still check to see if upvotes are coming on obviously VLQ or NAA posts, or posts that have already received a negative score: If so then yeah, it's probably blind. On the other hand, if every single post under that tag also happens to be a good post and now is also upvoted, not really anything wrong with that; at the very least, it makes it really difficult to distinguish "blind voting" from "enthusiastic but valid voting" without other supporting evidence.