Im assumeing that these holes are in your equipment, and they must be large enough for a rodent to crawl through, I think you need to have someone with more knowlege take a look at your "left over holes", you could have exposed electrical connections, and there are more appropriate ways of taking care of this issue...
In any enclosure, the manner in which a hole is filled should be, with respect to the NEC, of the same strength and integrity as the enclosure itself. The definition of 'a sealant' can mean a lot of things to a lot of people, but if you are referring to something that cures to form a rubber like substance the answer you are looking for is likely to be 'no'.
There are specific items to fill holes knocked out for conduit and not used. They are called 'knock out seals'. They come in several forms are are meant to be used in different applications.
What kind of hole in what kind of enclosure do you seek to fill?
Sorry for inadequate information. The holes that I mean is the entrance's cap cover which already provided from manufacturer ( Black Plastic Cover at Cable Incoming Side )