Josh,
I'm not familiar with all the US laws on the subject, but I believe the guy in the US who was recently fined did have an import permit and the best of intentions. If the country of export is a signatory to the CITES convention (and most countries are) then the plants have to be accompanied by a CITES export permit also, otherwise the shipment is in breach of international law and people at both ends are culpable. The guy who sent the plants can be prosecuted for smuggling (sending plants without due documentation) and if it can be shown that the importer "caused the illegal importation" e.g. offered money or other inducement to cause the plants to be sent, then the importer is also liable to prosecution in most countries.
I think this is what just happended to the guy I mentioned in the U.S. He was advised to plead guilty and fined several thousand dollars. The alternative would have been a long legal battle that would have cost far more than this in legal fees.
Don't want to sound as though I'm scare-mongering, but it's best to be careful not to make a mistake. Even an innocent mistake can be costly as ignorance of the law is no excuse.
Incidentally, in the case above the parcel was labeled something like "toys" or "clothing" so there was no doubt that it was an attempt to smuggle on the part of the exporter. The poor guy who was caught at the US end suffered the penalty and is kindly warning everyone not to get caught in the same trap.
Finally, I'm not trying to imply that your friend is dong anything wrong at all. Sounds like a great guy!