From what I can see on the web, then White House Chief of Staff John Kelly and Joint Chiefs of Staff Marine Gen. Joseph Dunford both attended; there are pictures here of them and their wives at the cemetery on November 10th. Undoubtably there were others in attendance as well, including the typical raft of photographers and media members. This was not the full ceremonial event at the cemetery, which was held previously on May 27 (and which Trump also did not attend), but was clearly a planned, official visit.
This article from Reuters, written at the time, states there was "light steady rain and a low cloud ceiling" which prevented helicopter travel, and that 'logistical difficulties' prevented the president from traveling the 50 miles to the cemetery by car. No foreign dignitaries that I am aware of had planned to attend the Belleau Woods cemetery on this date, but both French President Macron and German Chancellor Merkel attended an outdoor ceremony in Compiegne, France, which is roughly 40 miles northwest of Belleau Woods. This article says they stood "under grey clouds and persistent drizzle," though it's worth noting that all pictures of the event I could uncover lacked umbrellas, rain gear, temporary shelters, or any obvious signs that precipitation was significant.
I sincerely doubt a Marine helicopter pilot would have considered this weather too risky to fly in, though obviously the standards for conveying the President would be more conservative. However, I find it impossible to believe that the Secret Service did not have back-up ground-travel plans worked out in advance for just such an occurrence. And clearly the weather was not inclement enough to keep Kelley, Dunford, Macron, Merkel, and a host of other people at both Belleau Woods and Compiegne away, even though the first two had to make exactly the same trip Trump claimed as logistically impossible.
Per comments, here is an "Atlantic" article from November 12, 2018 that discusses the weather conditions in France on November 10th, down to the METARs (specialized aviation weather reports) for the day.