Okay, after reading through the thread, I'll distill this for the OP:
There are "sister companies" that have the same ownership or partnership situation. Some are a European/American affiliation, some are affiliations for other reasons. Innova/Discmania is one, Discraft/DGA is another, and of course there's the Trilogy of DynamicDiscs/Latitude64/Westside Discs.
Players sponsored by one company may have contracts allowing them to throw discs made by sister companies. This used to be more common, but the recent trend has been to encourage players to throw discs from one company only when possible. Paul McBeth used to throw some Discmania discs, but has given them up (unless he sneaks an FD3 into his bag on occasion). Eagle and Simon have streamlined their bags to be all-Discmania (or nearly so; Eagle has that Gator stashed in his bag). On the flip side, Ricky Wysocki is Latitude64, but that Westside Harp is not likely to leave his bag any time soon.
What you're not going to see is Paige Pierce (Dynamic Discs) throwing Prodigy discs, or Big Jerm Koling (Innova) throwing MVP, or Ricky (Lat64) throwing Innova discs. No affiliation or sister-company relationships there, and contracts would likely forbid such crossovers.