Do atheists have better chances of knowing the truth about God than theists?
If the Judeo-Christian-Islamic derived word "God" lacks a reference, if the word doesn't correspond to anything in reality, then my answer is yes. The "truth about God" would be that God doesn't exist, which is what the atheists have been saying.
If the word does have a reference, if something corresponding to 'God' does exist out there, then my answer would be... probably not.
If the existing God has already been revealed in one of our theistic religions, then the answer obviously is no. To know that God, one would need to drop their atheism and accept the true religion.
If the existing god isn't captured, decribed or revealed in any of our theistic religions, then that suggests two questions:
1. Does belief in one of the theistic religions plant somebody so strongly in an incorrect understanding of God that a correct understanding becomes difficult or even impossible? Are people so filled with faith in their errors, that they can't even recognize that their beliefs are errors? And are they so greviously misconceiving God that a correct conception becomes too alien for them to grasp? If so, then maybe atheists would have an edge since they aren't starting with all of the preconceptions.
2. But on the other hand, is the means of knowing "the truth about God" ultimately through intuitive, mystical or some other unconventional non-sensory way of knowing? (Assuming that such ways even exist, which is obviously an open question.) Atheists already have plenty of preconceptions of their own, and if they end up bringing an inappropriate epistemology to the table, then they might conceivably be putting themselves at a serious disadvantage.
And finally, bottom line...
Obviously if somebody rules out the existence of something a-priori, then they are unlikely to ever become an active seeker after that thing, let alone be the one to find it.