Yes, Chip Rommel from "Son of the Beach" is filling in for Arnold. I saw that Arnold biopic he was in and he played a pretty good young Arnold, he was much more believable than Jurgen Prochnow was as the older Arnold.
I notice they didn't mention Christian Bale is playing John Connor.
http://www.clintonnewsrecord.com/ArticleDisplay.aspx?e=1117058