The Old Glory DC hooker will be with the Warriors until the beginning of the USA club's debut Major League Rugby season.
The agreement comes off the back of the partnership between Scottish Rugby and Old Glory DC that was announced in March 2019.
Iscaro is a product of the rugby programme at the University of California, Berkeley, led by former USA Head Coach Jack Clark.
The Cal programme has produced internationals such as former Cardiff Blues and USA Eagles captain Blaine Scully, as well as the most capped USA international of all time Mike MacDonald.
Iscaro played his youth rugby with the Maryland Exiles programme and his high school rugby with Gonzaga College High School, where he helped to earn two National Championships.
The hooker, who is also capable of playing at prop, is a native to the DC area and will train with the Warriors until December 2019, before returning to Washington to represent his home club in their debut MLR season.