There were no Ranger units assigned to SOG; however, there were many members of SOG that were Ranger Qualified and assigned on an individual basis to SOG. See below comments - RLNoe

Rangers (LRRPS) were assigned to 2nd and 3rd Mobile Strike Force Commands by 1FFV and IIFFV rspectively. There were no comparable assignments to MACVSOG. Ranger qualified SF personnel were often assigned to MACVSOG.
Steve Sherman
MACVSOG/Vn SF Historian
There were many U.S. Army Rangers assigned to SOG.  That is, there were many SOG operatives who were Ranger qualified and had been awarded a Ranger Tab as graduates of the U.S. Army Ranger School at Ft. Benning, GA.  There were both officers and NCOs who were assigned to MACV-SOG who were Ranger School graduates.  I graduated from Ranger School in Oct 1968 and know that several other officers and NCOs who were in my Ranger class (Ranger 4-69) had previously been in SOG and also some who were later in SF and SOG.  You should understand that graduation from Ranger School did not necessarily mean assignment to a Ranger unit.  Also, not all members of Ranger units are graduates of Ranger School.  Many Infantry and other combat arms lieutenants as well as virtually all USMA graduates would graduate from Ranger School but would not necessarily be assigned to a Ranger unit.  I also served as a MACV advisor in the 37th Vietnamese Ranger Bn.  It was a requirement to have been awarded a Ranger Tab (Ranger School graduate) to serve as advisor to a VN Ranger unit.  However, there were no (to my knowledge) Ranger units ever assigned to MACV-SOG.  But there were many RAnger qualified officers and NCOs assigned to SOG.  Hope this clarifies it.  Please write if you have any additional questions.
Larry A. Greene
COL, SF (Retired)
We had a number of men at Omega and CCS as well as many in SF, who wore ranger tabs as they had been to Ranger School and graduated prior to RVN.
They were all airborne, then SF, plus they all volunteered for SOG with a few non SF volunteers. I recall one 75th Ranger being assigned to us from the Americal Div after he extended his tour and volunteered for SOG. Then the orders were issued assigning him to us. He was not SF qualified. He was airborne/ranger and ran recon at CCS. He was an LT. who came to us in August or September 68, then took his extension leave in January 69.  We also had one leg assigned to our S-4 shop.
While ar FOB 2 in 67-68 I inserted ranger recon teams in country in various locations thre head of the plei trap valley comes to mind.  I know of none physically assigned to a position in SOG.  Take care, I hope this helps.  
Hum,  if I'm not mistaken, I believe that a few SF types did go through Ranger school. I believe they wore the Ranger Tab but were SF.  I'm sure some were assigned to MACV-SOG...
     Jim Jones-Shorten, sends