It's most likely just PC12800 memory from one of the major manufacturers but it has been re-roll-marked, re-branded and distributed under the Integral name. This is common practice since most of the memory manufacturers prefer to sell in bulk to distributors and don't want to bother with retail sales. There are exceptions such as Micron Technologies who manufactures their memory and sells under their own Crucial brand. I don't know for sure but they probably still manufacture and re-brand memory in bulk for other distributors.
After you install the memory you can check the information about your installed memory under the OS X hardware system info and there is usually a manufacturer ID code for each memory stick installed in each memory bank. If it is re-branded then you can do an internet search and look up those memory codes (some internet sites have them posted) to see if it was made by the more common manufacturers.
Whether or not mixing your memory will work is another question. Be careful and test it thoroughly after installing since their have been many reported problems with different brands of memory installed on the new late-2012 model Mac Minis. Many of the problems have been graphics related since the late-2012 Minis use part of the shared system memory. As a rule if I can avoid it I try to never mix different memory modules and instead purchase matched pairs of the same brand but many people do mix different brands successfully and don't seem to have any problems.
If you want to mix different memory sticks you ideally would want both to have the same voltage and CL settings. It still might work if there are differences. You might have better initial results if try putting the stock memory in bank 0 and add the new memory in bank 1 (from various user posts in this forum I believe the shared video memory is utilized from the stick installed on bank 0) but after testing your system the first way go ahead and try swapping the sticks around anyway just to thoroughly test the compatibility of the new memory in both banks. Remember to always be patient and careful when changing out the memory sticks in the Mac Mini.
