I mean it's a series with a flying guy with lighting eyes in a giant straw hat, multiple palette-swap ninjas who look nothing like ninjas, a guy who punches people in the nether regions for fun, and an off-brand parody of Bruce Lee.. It's not meant to take itself too seriously, and that's part of the charm. I'm sure the acting will be fine for the tone of the series.
Yes MK is not super serious, but it still very serious for it's own and sure as hell more serious then any other fighting game series. All of the less-serious stuff in MK are related to specific things during gameplay like the Test Your Luck modifiers as well as some finishing moves like the Friendships. And yes, only some, because most of the gameplay elements are also very serious, and when it comes to the actual story, it was always more serious, and not just in recent NRS games like
@HeavyNorse said. Arcade endings in the Arcade mode are for the most part "what if" scenarios rather then canon endings, but even for non-canon endings, almost non of the endings in all of the MK games were comic related or cheesy. Other then Johnny Cage's ending in MK4 as well as Stryker's ending in MK9 that also involved Johnny, all of the endings for all characters in all of the games were serious, canon or not, unlike the Tekken series for example which all of the characters were comedy-prone, including the Mishimias who are suppose to be the main characters of the series. Hell, Lee's ending in Tekken 5 featured Heihachi Mishima with nothing but a tiny underwear and a bow tie. I can't think of any MK ending or any story mode cutscene in any of the MK games from MK1 until now that was even close to be as cheesy as that.
And speaking of characters, all of the Ninjas in MK were looked like Ninjas from the very beginning, and even after all of the changes to their designs you can still clearly see their Ninja elements, Raiden hat doesn't take anything from him being a Thunder God, Liu Kang is Bruce Lee-inspired character and not a parody, and even Johnny Cage being the only true comic relief character in the series still can sow some elements of seriousness, as we have seen in his interactions with Sonya and others in the MKX story mode.
Even if the story was cheesy (and it's not), voice acting is a huge part of what makes the story of the game and it's characters so appealing to the fans and the masses. NRS/WB know that and that's why they make sure that they voices will always hit the nail with whatever characters they're voicing, and it always worked for them, regardless it's cheesy or not. So if something is cheesy, the voice acting still needs to be on a high level, except that, once again, it's not cheesy.
So they are indeed gonna keep the voice acting true the series, both in terms of quality and direction of the series.