If your wondering if they are legal why not contact them rather than a forum that really has no way of knowing and can only assume. ?
If I was that company and saw that you posted a comment saying we were probably doing illegal stuff I'd come after you for defaming/slander/etc.
Sounded in your post more like you were wondering if you could get away with it for tshirts.
I have no intention on messing with their bussiness. This was just an example, there's tons of sites like this.
I don't want to make shirts with logos like that, but it is a little frustrating when you're trying to be legal in every detail an them come upon a site like this.
What had me wondering most was the idea of theoretically contacting each and every company asking for their consent - that was clarified by Tim.
This is what I found in the copyright info of a different site (they offer Puma, Barbie, etc. vinyl logos)
All materials published on this website are copyrighted. Products and services listed on the site, information about them and their images may be protected by other rights of individuals. Names and designations of products, services, companies, and corporations may be registered trademarks of their respective owners. WARNING! All logos are trademarks of companies or products and are their exclusive property. The purchase of these goods can not be considered a trademark property for the buyer. Ownership of registered trademarks is not transferable and purchasing these goods does not automatically entitle to trademark use.
Pretty much makes no sense to me (in regards to what they're doing).
This is also interesting (from above site):
Some of the logos included on this site are the trademarks or registered trademarks of their respective companies and are provided as a convenience only for their lawful use. It is the expressed intent of xyz.com that any unauthorized use of these items by the purchaser shall be the sole responsibility of the purchaser. The purchase of any item from xyz.com is not authorization for the use of any specific logo or trademark. By purchasing said logos, you are indicating that you have authority to use the artwork.
What I think they're saying is, if you come to our shop (let's pretend there's no web site) and want and XYZ logo, we'll cut it for you, but you agree that you have the authority to use it. The shop isn't obligated to check who's logo it is, so they assume its the customer's.
Am I just making this more complicated or is my notion correct?
One more edit:

I remember back in the day it was legal to make copies of music/game/movie CDs, as in offering it as a service to someone. A customer brought an original Metallica CD to have a copy made for his own use, and the "CD burning company" made one, assuming that the customer had bought the original and has the right for a copy. Later the laws were changed, allowing you to make a copy only if you purchased the CD
and the burner was you property. Thus making the
service to copy illegal. But by that time burners were so cheap, the usual PC user was able to buy one, therefor making the service uninteresting.
The above seems to me like something similar.