Can our unit can force an NCO to do his DLC when he is getting out in 5 months?

No one can physically force the Soldier to do anything. But they can certainly put them on Staff Duty and CQ every weekend until it is complete. It is mandatory training, so any complaint the Soldier may have about unfair treatment probably won't go far. On top of that, these 8K DLC/SSD Bars are tracked all the way to HQDA and briefed by name and status in command and staff slides at every level. Because there are Generals asking why SPC Snuffy hasn't finished their DLC yet, your command team has an incentive to make it a priority.
As a leader it benefits your Soldiers to "encourage" them to complete their DLC even if they are separating. First, you can now take your promotable status with you into the Reserve Component. Second, you can't get a bonus going into the RC if you have an IMREPR code of 8K. Third, they receive an RE3 code on their DD214 with an SPD code saying they were barred. The amount of hoops you have to jump through to find paperwork proving it was an HQDA Bar for SSD and not a Commanders bar is ridiculous. Everyone who gets out swears they're never coming back in, but many of those same guys are calling me 90 days later to help them get back in.
In short, it doesn't hurt the Soldier and it may even help them to complete DLC.

If a SM fails to complete their respective DLC/SSD for the next grade prior to entering their primary zone for promotion, they will be barred from reenlistment by HQDA

Can't force him, can bar him for refusing to go.