A MOD is basically just a modification of exsisting units and buildings or perhaps all new ones. When you start a mod from the game browser you start up the main Execetuable from the original game telling it to run with a the extra/modified units that the mod adds to the game.
So basically yes. You
should be able to run a legal game with a NoDVD crack even if you run mods.
Here's another suggestion: Since you appearently run a network try this:
Right-Click your DVD-ROM drive in your machine and select "Sharing and Security". Choose to share the root of the drive (ignore any warnings. No one can change the data on the drive anywho).
Physically disconnect the faulty DVD drive from your sons machine so that it dosn't show up in the system.
Now go to your sons computer and right-click "My Computer". Right-Click and select "Map Network Drive" and find your DVD Drive on your machine. (if your computers name is "harry" and your DVD Drives Sharename is d the adress to the drive would be this:
\\harry\d). Make Sure you assign the drive letter that the faulty DVD drive had to the new drive, and voila: When you put in the CnC3 disk into your drive he will also have a "DVD-Drive" with the CnC3 disk in it.
Need assistance to do this?!? Write it here.
This is in my opinion a better solution since you wont have to download some No-DVD crack from a unreliable source that could contain Viruses or Spyware. Also: you can download 100 "Cracks" and none of them work. Usually you cant update CnC3 with a No-DVD crack either.