Well, what is true is their votes routinely get challenged and dumped by democrat lawyers in battleground states like Florida where they may tip the election.
Yes, the Gore team in FL tried to exclude military votes because the law required a postmark by election day. Since most deployed military mail is sent postage free via mail pouch, Gore's lawyers challenged every single military vote not bearing postage.
Only after they figured out Gore was losing did the Dems agree to allow military votes, because by then those votes couldn't hurt him and may have helped him however unlikely. They concluded if they were going to lose, they might as well defuse the anti-military vote accusations and let them be counted.
The party that fights against voter ID laws because of disenfranchisement has a history of disenfranchising the military when it is in their own self interest.
If I remember, several key states were very late sending out military absentee ballots during the 2012 Obama reelection. Nothing was ever done to punish the state officials for breaking those deadlines, since Obama wasn't about to slap the hand that helped him.