Holmes is a very good vertical receiver who totaled over 2,000 yards in his four years in New York all of which he was catching passes from Mark Sanchez or Geno Smith. While he doesn't have deep ties with Whisenhunt, they did have passing contact during Santonio's rookie year.
Holmes doesn't have to be the #1 receiver on the team or even the #2, but with Washington getting older and Kenny Britt, Damian Williams and Kevin Walter gone where is the depth in the wide receiver group? Holmes has some off the field issues that have made him unappealing to some teams, and other teams question his price tag, but if the Titans could bring him in on a two year deal similar to what they did with Shaun Phillips, then they could be getting a bargain.
If McCluster is really going to be a running back first, then Whisenhunt could use a receiver capable of taking a screen one play, and then taking the top off of the defense the next.