Akkerman inks are not made by Diamine. When I talked to the great folks from Vanness at the DC Pen Show, they call Akkerman the European Iroshizuku. I've used Iroshizuku and Akkerman in vintage fountain pens with very good results. But if I were to play it safe, I'd follow the advice given above and use inks made by the manufacturers who have made fountain pens for decades.
Well, here in Europe it is a very common opinion that akkerman inks are diamin re-bottled.
Beside from this common opinion, there is a strict relation among the colors of the 2 brands.
I visit from time to time akkerman shop in Den Hague, and I really have the impression that it is not produced from them in-house. Offen they also are sold out in the shop of some colors, which also mean a certain rigidity in the management of the stock, normally not typical of products produced in-house.
About Pilot iroshizuku, it has not too much to do for me with akkerman assortment of colors. Also smell and behaviour of the Ink is quite different.
it will be also quite complicated for an European company to import an ink from Japan, with all the relevant difficulties given by custom, when they can get supplied from inside EC.