The agreement - which got a 82.2% vote in favour - gives staff protection over their terms and conditions, including pension rights for three years from the date of sale.
It also guarantees that there will be no compulsory redundancies for the first 12 months.
SIS has also accepted that existing BBC redundancy terms will apply to anyone made redundant until December 2012.
Assistant General Secretary Luke Crawley said: “We have had constructive meetings with SIS and expect to develop a good working relationship.”
The voting turnout was 38.7%.
The sale of OBs and the transfer of staff from BBC Resources to SIS is expected to go ahead from tomorrow (1 April 2008).
Separately, BECTU has registered a dispute with the BBC over its failure to provide guarantees for staff in studios following the sale in 2012; the same dispute will apply to BBC Post Production if it is also retained by the corporation.
The union is expecting a response from the BBC early next week.