Eric. as I understand it, you are Orthodox. Well, "veneration" means the same thing in both faiths. I was Eastern rite, or Uniate.
Karl is worthy because he was known to be a "peacemaker". I am sure you know his history. In the Roman Church, he is worthy and faithful, but not a conduit to pray to. [or through. to be theollogically correct] So, it is OK to light a candle in his memory, just as one might do for anyone one admires. However, he is not to be expected to intervene in your prayers.