From what I know Zachariadis was pro-Stalin (hence he got purged later), although I have a more negative image of him compared to other communists (he purged EAM leader and Marxist-Leninist Velouchiotis as far as I know). But yeah, the USSR was reluctant in its support although it let communists in exile in after the Civil War's end. The countries which openly supported Greek communists were Albania and Yugoslavia.