They did until last year. David Bingham was loaned to San Antonio in 2014 and Khari Stephenson was loaned out to the same club in 2015. Don't see how or why they wouldn't do the same with SF.
The Indy Eleven had Charlie Rugg from the Galaxy, Dane Richards from the Red Bulls, and Zach Steinberger from the Houston Dynamo all on loan last year.
Also had Jimmy Ockford from Seattle in 2014, Leo Fernandez from Philly and Kharlton Belmar from Portland last year.
I believe SKC had 2 players in San Antonio last year (Kempin and Saad Abduul-Salaam) and one in OKC (Medranda) before needing to call them back due to injuries.