This came up last time we played. Can a revealed (and infiltrating) cylon play a strategic planning on a roll by the cylon ships activated from a crisis or another revealed cylon player at the cylon fleet. So I guess the question is can cards be played to modify dice rolls that don't benefit the humans?

Yes. A strategic planning can be played to modify cylon attacks, etc.

Clarifying the frame of your question, however, a player who is a revealed cylon (was dealt a "you are a Cylon" loyalty card and activated its action) cannot infiltrate. Only cylon leaders are allowed to infiltrate (Cavil, Caprica Six and Leoben, chosen at the beginning of the game). An infiltrating cylon leader or a Cylon who has not yet revealed can still Strat Planning or Calculations roll in the cylon's favor. Also fun: they can play evasive maneuvers to make raiders re-roll attacks that they'd missed.

This is why Cylon Sharon is fun post-sleeper when the airlock's broken.

If they're using the Sympathetic Cylon variant mechanic to replace the Sympathizer card, the Sympathetic Cylon is a revealed Cylon player that can infiltrate.

As already mentioned, regular revealed Cylons can't do that.