I found the text at Letters of Note; Correspondence deserving of a wider audience.
Here's the post dealing with Gandhi's letter. It turns out Gandhi didn't really know Hitler and was trying to butter him up and ask him, oh-so-politely, not to start a war. Well...that didn't work out....although the post makes mention of the fact that Hitler never actually received the letter. Still, I doubt Hitler would have cared about Gandhi's opinion. The letter was written before the start of WWII as tensions were ratcheting up in Europe but before the scope of what Hitler was eventually planning on doing was fully understood.
So....it is factually true that Gandhi called Hitler "my friend" but not thematically true that Gandhi viewed Hitler as one of his best buds.
Just an interesting tidbit I ran across.