The only source I know of for dieselpunk fashion is Gearing Up http://dieselpunk.net/ The problem is that while the site is great for showing images it doesn't do much for providing a definition of style.
Tome, I think you and I agree on this. My challenge is trying to find a source. I'm learning from reading the various Wiki material the amount of verifiable sources help in determining an article's "notability."
I may have to use a variation of your wording and Gearing Up and the discussion on this in The Smoking Lounge as sources.
I'd imagine the punkiness of Dieselpunk's style inspires the participant to "riff" on the extant styles from the era and provide a unique twist.
In both Diesel and Steam, there is something of an emphasis on accessories. The "punk" nature of both subcultures comes from expressing a more complete, so to speak, presence in public--where today's average fashion neglects much of yesteryear's requirements (such as waistcoats, covered arms, hosiery, styles of shoes, and headwear, to name a few), Diesel and Steam both emphasize the inclusion of such accoutrements to render one's look "complete," in defiance of modern custom. This extends to the visual media aspect of the subculture, where a photo shoot or visual presentation not only includes the wearables, but also includes appropriate venue and complimentary properties.
The fashion also extends in some cases to the manner and custom adopted by the wearers of the fashion. Proponents display courtesy and manners appropriate to the era (whether expressed historically accurate or historically fanciful), in order to further round out the dimensions of the expression.
This is not to say the proponents adopt in-period "personae" although such an element does exist and is enjoyed by many within the subculture. Dieselpunks and Steampunks are not costumed re-enactors or players, except in certain cases where they are. ;)
Sorry...I slipped a little there into nerd-mode. Hope you don't mind.
Having said that, check out some Alexander McQueen as influenced by steam and diesel. The designer has, alas, passed on, but elements of his style have demonstrated distinct *punk influences.