I think Leeteuk will have to serve, but I'm not so sure about Heechul.
Here'a a post from the blog Ask a Korean. It's part of a series explaining the military in South Korea.
The question of “where you go and what you do” clearly is the most important one. Obviously military involves fighting on the frontline – and Korea has a long frontline against North Korea. To determine the assignment, all Korean men over the age of 18 must report to the local draft board to have a physical examination. The examination categorizes men into seven levels, and people below Level 5 do not have to serve in active duty.
Achieving Level 5 and below is fairly difficult; you really have to have some severe injury, such as a torn ACL, missing index finger, serious mental illness etc., to qualify. However, there are certain non-health related issues that would disqualify one from serving, generally described as “people who would create disharmony in the unit.” Interestingly, another group that falls into this category is people who have excessive tattoos, because tattoos are generally considered a sign for a gang membership.
Heechul would easily be able to get out of having to serve because of his homosexual tendencies. I'm not sure if he's actually gay or not, but I'm convinced he is, so I'm thinking he won't even have to serve. He would create disharmony because the other soldiers would be worried about Heechul buttfucking them or some shit.
But the thing is, would South Korea even want Heechul to be a soldier? I have the feeling that Heechul would get raped by a North Korean soldier if there happened to be a war while he's in the military because the NK soldier would probably think Heechul is a girl.
The only way I could see Heechul being useful at all is if South Korea made a special forces unit composed of Heechul and Kwanghee. Have the two infiltrate North Korea and carry out their plan. They'd dress Heechul up as a woman and try to get him to seduce Kim Jong Un (Kim Jong Il's fatass son next in line to be ruler if you didn't know. I swear, seeing how fat that fucker is, he probably stole food from about 1 million of the commoners in NK.)
Kim Jong Un and Heechul would be having a romantic dinner together. Kim Jong Un would probably have to resort to drugging Heechul to get him into bed. After Jong Un would take off Heechul's pants, he'd shoot Heechul for having a dick and then shoot himself because he got trolled by Heechul.
Oh, if you're wondering what Kwanghee's mission would be, it would be trolling by mere existence aka what he already does now. He'd be trolling the NK soldiers so much that they'd probably commit mass suicide or some shit.
No funny pictures in this article, sorry. I saved them for the tumblr.