Thank you for catching that error and posting the correction.
You’re right, it should read “Type 91” 105mm howitzer, not “Type 38 10-cm field gun,” the latter which is a completely different weapon that looks like this (from Taki's excellent reference site on IJA equipment): http://www3.plala.or.jp/takihome/38-10.htm
However, since my sources all mention the name "Type 38," I am currently researching the possibility that official Nationalist Army records of the time actually call the IJA 105mm howitzer a “Type 38 field gun,” instead of “Type 91,” for reasons to be determined.
Details on the Nationalist Army's use of modified M10's will be elaborated in another post.
To answer the original post, in conclusion:No
M18 Hellcats were used in mainland China. The Nationalist Army only used them on Taiwan after 1952.
On a lighter note, M18's also appeared as Japanese Army tanks in Chinese-language war movies filmed in Taiwan, such as the 1977 Taiwan war epic "Heroes of the Eastern Skies" [筧橋英烈傳], and the 1976 Hong Kong Shaw Brothers martial arts epic "Seven Man Army" [八道樓子; based on the 1933 battle of Badaling along the Great Wall]. At present both titles can be found in their entirety on Youtube.
The only self-propelled guns based on US-supplied vehicles used in mainland China during the Civil War period may have been modified M3A3 Stuart tanks fitted with fixed-mount M1A1 75mm pack howitzers (not M8 "Scott" Howitzer Motor Carriages, which were used only on Taiwan), similar to what was used by the allied-trained Provisional Tank Groups during the northern Burma campaign of 1944-45, but in unknown numbers.
Hope this helps,