Yes, both were used by the USMC in the Pacific Theater. My sources are vague as to actual dates and locations of deployments beyond vague references to "late 1944." The piece regarding the M-8 states that due to armor improvements in later production blocks of Germany's Puma armored car, the Greyhounds were sent off to the Marines.
"Subsequently, many of them were shifted to the Pacific theater in late 1944, soldiering in the Philippines and Okinawa, where they even reverted back to tank-hunters. Around 1000 were also sent, through Lend-Lease, to the British, Free French, and Brazilian forces."
The case is similar with the M-7 Priest. Changing technology was shortening its service life in Europe, so it too began Marine Service in "late 1944", in time to see service in the Philippines and Okinawa.
Edit: The 105mm M7 self-propelled howitzer was first used by the Marines on Okinawa. (G-Series Table of Organization and Equipment states that "each infantry regiment (was) equipped with four M7 HMC's in the regimental weapons company" at Okinawa.
This page has a decent table which lists the USMC tank battalions of the Second World War by campaign and type. Hopefully, it helps with your future research.
http://mcvthf.org/History/Evolution_of_Marine_Tanks.html