Arkadi, information you are looking for was posted at the Russian web-forum, dedicated to WWI and civil war in Russia. Most of those, who took part in this discussion, agree, that:
1) There was NO general-leitenant of the Russian Army with the surname Rakoff (Rakov). No one of the lists of generals, including those, who were promoted after 1917, contains his hame.
2) Probably, the general' sone changed (or modified) surname, when escaping from Russia.
3) Definetely, he escaped in 1920 (not in 1917/18); Russian 'white' warriors were evacuated from Krimea to Konstantinople in the autumn of 1920.
My suggestion is to use the genealogic information you have (at the Russian forum somebody have mentioned the wife of the general surname Ignatieva), and search in the archives for the address books of St. Petersburg, etc. Same for Rakov.
By the way, you can try at the Russian 'genealogy tree' fromum; they also mantain a part in English (www.vgd.ru).
If any relevant information will be discovered, I will let you know.
P.S. My grandfather was a general of Russian Army, killed in 1918. I have discovered his biography mainly with the help of www resource, where request regarding your ancestors was recently posted (www.1914.borda.ru)