So I work in Human Resources (for a different company), but we do host an employee survey every year (similar to Target's BTS).
While I can't speak for Spot's vendor, the survey results we receive are completely anonymous. While we do require employees to login to the system to take the survey, it's only used to ensure that employees aren't repeatedly filling out the survey (like, if they totally hated their boss and filled out a survey 10x to skew the results), and to prevent managers from making their results look better.
We only receive the test feedback.... We don't know who took the survey, who answered what, or who left comments. The survey company doesn't provide that information, and our vendor representative is always very adamant that they wouldn't provide that information anyways.
In fact, if a supervisor has less than 10 direct reports, we don't see the breakdown of scores (or the comments), just the overall %. For the free-form comments field, the results are edited, so managers familiar with the way his/her team members write wouldn't be able to figure out who wrote what by the sentence structure, misspellings, grammar usage, etc.
Your results should be safe.