The solder really is not gonna be a problem, they have to construct them somehow. The flux on the other hand, mainly water soluble, is what comes out when you do the rad dance. The old Thermochills were notorius for a ton of flux. Very hard to get clean. Agian, the tin in the solder is not a problem, you will have most likely replaced everything a few times over, the computer would be obsolete, before the solder would cause a galvanic issue. AS long as you have not run some sort of S*** a** concoction thru the loop.
The Admiral rad
You need to check independent reviews on that. I would suggest AMS radiator
if you are worried about solder/flux. Admirals have horrid restriction, and sub par performance. Plus the in/out ports shoot straight out the bottom, no optional configs. Oh and the SS wouldn't be a problem, except for heat transfer, most blocks have a SS jet plate in them. Last comment on Admiral, goes for AMS too, the fins are aluminium, but that does not have any fluid contact, so it's a non issue.
I found something interesting, and pretty simple terms that discusses plating corrosion. Here is the source.
What causes metals to oxidize or “rust”?
All metals, with the exception of the precious metals, will oxidize when exposed to oxygen and an electrolyte (i.e. atmospheric moisture). It is a chemical reaction of the metal surface with the oxygen present in the air that causes some of the metal to corrode (or oxidize) and form the respective metal oxide on the surface. In some metals such as steel, the corrosion products formed are very visible and loose. Everyone has observed the red color of iron oxide (rust) seen on improperly protected steel products. The red rust formed is generally scaly and loose and easily falls away exposing more and more basis material to the environment. However, metals such as stainless steel (steel with added nickel and chromium) oxidize as well. The difference is that the nickel and chromium oxides formed are a more uniform and tenacious oxide layer that protects the underlying material by “sealing” the surface from further oxidation once formed.
In addition to the surface oxidation that occurs on individual metals, any two dissimilar metals placed in contact with one another with an electrolyte (such as atmospheric moisture or water) will form a corrosion cell. This is the very basis of batteries used in everyday products. One of the two metals in contact will corrode in preference to the other and form that metal’s respective oxide. Which metal corrodes is based on what chemists call the electromotive series of metals. The selection of what plated layer to use is an important one since electroplating in its very essence is the process of placing two dissimilar metals in contact with one another. The plated layer (or layers) can either be an anodic coating (coating corrodes in preference to the substrate) or cathodic coating (substrate corrodes in preference to the plated layer). Whether a coating is an anodic or cathodic coating greatly impacts how the finishing system will perform once in service and there are advantages and disadvantages to each.
Read the full quoted source, and it explains flaking of nickel pretty good. Anyhow there will be more opinions and quotes and such.
Found one more interesting read, it's a pdf but on page 11
it describes the resistance to corrosion of electroless nickel or salts, CuSo4 which is PT Nuke or copper sulfate.