It looks like they did work on PC for awhile, but something broke mid-Aug.
From http://deadspace.wikia.com/wiki/Downloadable_Content_for_Dead_Space_3 :
"Note: As of August 17th, 2013, a bug for the PC version of Dead Space 3 may prevent some users from obtaining resource packs, which have disappeared from the DLC menu."
Another thread on this issue with the same name which has info in the OP about what EA is doing to resolve this: http://answers.ea.com/t5/Dead-Space-3/PC-BUG-REPORT-Cannot-spend-Ration-Seals/td-p/1411946
Same issue. Unable to use Ration Seals at all from either DLC main menu or Benches.
