Aah - that old accuracy bugaboo.
While the Americans began providing Lend-Lease to Russia in June 1941, did any Jeeps make it all the way across Russia, on a one track railroad, to the far eastern end of the country in time for the Doolittle raids in early 1942? This was away from where the fighting was to an area were there was an uneasy peace with Japan. Remember that Russia did not enter the war with Japan until August 1945 (or was it very late July).
The attached link says that the Bantam version of the Jeep began arriving in "late 1941" and that Russian copies of the Jeep were reserved for ranking officers until their numbers were sufficient for general use.
http://wmspear.com/Bantam/bantik.html
Was there an American-made or Russian-copy of a Jeep on the field in Vladivostok in April, 1942? I would say that it was unlikely, however it is difficult to prove a negative.
For historical accuracy's sake - make your diorama in accordance with a photo or other documented references. That being said - it is your diorama and complete it as you prefer.