It doesn't make sense to assume that the RMP (police in Iceland) failed to follow Icelandic law. Especially when the memorandum you linked says they followed local law and applied for a warrant (or so).
Subsequently, after obtaining the legal process required under Icelandic law to search the server, and after consulting with U.S. authorities concerning the timing of the search, the RMP covertly imaged the server and shared the results with the FBI on or about July 29, 2013.
It's certainly possible that the memo is full of misrepresentations or that the FBI mislead the RMP, but I don't think it is so likely that it should be assumed to be the case.
Subsequently, after obtaining the legal process required under Icelandic law to search the server, and after consulting with U.S. authorities concerning the timing of the search, the RMP covertly imaged the server and shared the results with the FBI on or about July 29, 2013.
It's certainly possible that the memo is full of misrepresentations or that the FBI mislead the RMP, but I don't think it is so likely that it should be assumed to be the case.