I don’t think (translate to ‘IMO’) that anyone trained in classical flute would have a hard time playing the wooden flute. Sounds like a wood flute myth designed to make us (wood flute players) feel superior. It may take a few minutes to adjust one’s blowing, but this would be true of any new flute, silver or otherwise.
Mind you, I’m talking about technical ability. I do agree with Brother Steve that technical ability does not equate to good Irish music playing. But the wood flute isn’t just used to play Irish music so it’s important to define what we mean by playing.
As to the best way to start, I would say this. If you ever want to be able to play chromatic music well on a Boehm style flute, take lessons from a classical teacher. It’s very easy to take Boehm finger to the woodflute, but more difficult to go the other way.
It’s like learning to drive on a stick shift. If you learn stick, then it’s fairly simple to get used to the automatic. Sure, once in a while, you try to clutch the invisible clutch, but for the most part you do fine. If you learn on an automatic, it takes time to figure out the stick. And until you do, it’s a pretty jerky ride.
That said, don’t take Boehm flute lessons to get better at the wood flute. I would think that most classically trained flute teachers would be more than willing to teach you on a wood flute. Most good teachers that I know actually have an interest in the older Baroque and Renaissance wood flutes.
If there are Irish masters in your area (and you are wanting to play Irish music) then that would be even better.
Also, I thought that I would dispell the vibrato myth. There is nearly as much controversy surrounding vibrato in classical music as there is here in C&F land. While it’s generally understood that there should be some vibrato, many find it’s overuse annoying. This is one reason that some don’t like Galway’s playing. He uses vibrato extensively.
I would apply this to the whistle and Irish flute as well. I like the sound of moderate vibrato. Used appropriately, it will sound appropriate. I like to use vibrato on long sustained notes. But I must agree that it is difficult to break the vibrato everywhere habit. For example, it doesn’t sound particularly good anywhere on my Overton Low’s. The oscillation creates a scraping sound.
Sorry, not much of a denoument, but I’m done writting 
Peace,
Erik