I do not know if having multiple Damage Control Modules stack their bonuses and if they do, if it's a meaningful advantage. If you have none of them, any repair will take hours. If you have one, it is cut down to minutes. The improved and advanced versions offer a better bonus. The wiki is wrong when it states that "Usually that works out to some hours, although a very large number of modules could shorten this time considerably" because even a single module will cut down the repair time significantly. Considering how much space they take, it isn't practicable, in my opinion, to stack DC-modules.
Furthermore, the wiki article that you linked did not specify whether DC modules help with parasites. They are automatically repaired in any case, just by being in the hangar. I do not know whether the host ship Damage Control Rating affects that.