Dark vileplume, again.

[linkez]

people told me that supporters now are no longer trainer cards

(example: http://pokebeach.com/scans/platinum/109-looker's-investigation.jpg)

so i'm asking again if they will not be able to be played, since people is telling me you can play supporters.

thanks again, linkex

[PokePop]

They are wrong.
Yes, Trainers split into three different types with the release of Diamond and Pearl, but Dark Vileplume is from before that time and the rule book when D&P came out stated that older cards will continue to treat all three types of cards (Trainers, Supporters, and Stadiums) as Trainers for their effects because that is what they all were when those cards were designed/released.

This is an official ruling; not a guess, not a feeling, not an opinion.
PokeBeach is a great site for information about new cards, but for rulings advice, this is the place.
It's also good to use the Compendium LvX as your primary source.
Here is the section on Trainers in General: http://compendium.pokegym.net/compendium-lvx.html#34

You'll note that this ruling is the first ruling in this section and we highlighted it in red for it's importance.