They do represent a push to solidify training camp competition, if not add depth to the 53-man roster.
At least with the two linebacker candidates, Johnson and Roth, the Steelers could use some depth, and both Johnson and Roth could be spot starters.
Having a player like Johnson, a savvy 4-3 outside linebacker who would play inside in Pittsburgh, may have helped the Steelers midway through last year, when James Farrior went down with injury, and depleted their ILB depth.
Roth seems more of a viable candidate to join the team than Johnson or Rayner (probably just a lead horse to push incumbent Shaun Suisham, who's contract is probably too much to jettison, but the savings aren't enough to bring in anyone significantly better than he is). A tough, heady player, Roth has battled some injuries while playing on doormat teams throughout his career (Miami, Cleveland and Jacksonville).
It wouldn't be surprising if the Steelers may look at him as a defensive end (which is what he played in Miami last season) but likely, in the event of his signing, he'd be an insurance policy on the prize OLBs the Steelers currently have as well as solidify depth behind their young defensive ends. He can contribute on special teams as well.
Johnson, though, has a great combination of size (6-foot-5, 245 pounds) and experience (64 games played since 2008, all with Cincinnati), and could help push Stevenson Sylvester as the buck back-up to Larry Foote.
Both Roth and Johnson are the right kinds of free agents the Steelers should be looking at; Roth in particular. He's big, tough and nasty. He can get after the passer as an OLB in a 3-4 defense, and holds up fairly well at defensive end.