It says aluminium but most radiators of this formfactor use copper channels internally so you can never be sure. The barbs are also [strangely] listing as having copper, so I wouldn't risk it.
If I can't use silver, can you even use DI with the proper additive? PT Nuke, something else? I would think the DI is the most reactive liquid possible to use since it is stripped of mineral ions.
What is the BEST thing to use with the lowest amount of maintenance?
PT Nuke [which was replaced by PM Nuke wasnt it?] is just a biocide, its not going to stop the water corroding. Your best bet, as recommended is to get a premix coolant. Yes it costs $10 a litre, but its $10 rather than potentially having to replace $100 of components.