First, there are "degreasers" and then there are "DEGREASERS". Mild degreasers like Simple Green are o.k. to spray on and scrub or wash off. But strong degreasers (like automotive engine cleaners) can damage components and should be avoided. Even Simple Green can take the finish off aluminum parts if soaked or sprayed and left on for too long.

Second, do NOT soak the free hub in anything. That's overkill. The internal springs and pawls are lubricated with a light oil, which would be likely adversely affected by soaking in a degreaser. The rubber seals could be damaged as well.

Third, soaking your derailleur in degreaser is overkill, too. There are bearings in the pulleys that would have to be dis-assembled and re-greased as a result. A small brush (like an old toothbrush, or a grout brush, or Parktool's drive-train brush) are all that's needed to clean the parts you want to clean.

Other than soak-cleaning a chain or cassette, there is little reason to soak-clean any other parts, including the ones you mentioned.

Bob