Plastic Plugs in Surge Protectors or UPS
The plastic plugs will in no way change the electrical functionality or behavior of the surge protector or UPS. 

There is one thing to think about though. The plastic prongs on the plastic safety plugs are generally thicker than the metal prongs on a typical power plug. When the safety plug is inserted into an unused outlet the plastic prongs will spread the electrical contacts in the outlet more than they normally would be. For quality outlets this presents no particular problem because the range of springiness of the contacts is plenty capable of retaining its contact pressure even after the safety plug is removed. However there are the ultra low quality outlets, especially those on the cheapest plug strips (whether they have surge protection or not), that can become deformed when the plastic safety plug is inserted and/or left in place for a long period of time. Outlets with deformed contacts can cause heat buildup, intermittent connections, and potential plastic melt down or even a fire.