Hiring minorities has shown to be a constructive way for WWE to draw in larger audiences from other countries. WWE has expanded into India, where I think they have a fairly significant audience, which is why Khali & Mahal are still on the roster. Same with Sin Cara & Del Rio in terms of Mexican audiences. At the end of the day, however, WWE's bread & butter ultimately comes from the United States. With whites & blacks making up the vast majority of the US population, it stands to reason that there are going to be more blacks & whites on the roster.
However, if you're someone who doesn't have a good mastery of the English language, then you're probably not going to be a major star in any American wrestling company. You have to be able to connect with the audience in order for them to truly care about you. That doesn't mean that they won't enjoy watching you wrestle if talking isn't your strongest suit, but it also means that the odds of you becoming a major player are extremely long. Khali can't wrestle and can barely speak English, yet he tends to get pretty good pops whenever he comes out. Whether it's Raw or SmackDown!, he gets a good reaction from fans. Sin Cara, whose never spoken a word in WWE, generally gets the crowd going during his matches, but I don't see him as the next Rey Mysterio. If I'm not mistaken, Sin Cara is already out injured after recently coming back from injury. Same thing with Mysterio, yet Mysterio is someone who has remained consistently popular since his days in WCW. He's a top merchandise seller in WWE as well, so Mysterio is someone who clearly brings a good amount to the table. In the case of Alberto Del Rio, WWE officials like what he brings overall. He's not the best on the mic and his thick accent can make it hard to understand him sometimes. But, Del Rio is someone who has a good look, is getting solid reactions from the crowds and is strong inside the ring. He can brawl, do the high risk stuff and he's a legit mat technician. He has enough of a total package in the eyes of WWE officials and that's why they've pushed him so hard since coming to the company.
As for TNA, like WWE, most of their minorities are black or of Hispanic descent. Many of them haven't really connected with the audience in terms of characters but, like in WWE, they still get good responses. For instance, Chavo & Hernandez are dull as dishwater as characters, yet they get good pops.
At the end of the day, being a minority these days can help if you're a wrestling company as large as WWE and TNA. Both companies have big audiences in foreign countries like Mexico and India, so it's natural that they'd like to have stars from those countries on their roster. But that's no guarantee of stardom, not by any stretch.