The Football Record for rounds 10 & 15 that year has Whitten as no. 22 on the complete list of players page (he wasn't named in the actual lineup). However, Smith is shown with 8 in the round 7, 14, 17, 19 and 21 Records. One of the commentators didn't know who Smith was, so I presume they weren't expecting him to be in no. 35 in the game against Footscray.I think you are right - Low does look a lot like Mystery Man, who you get a good look at at 15:10 in the last quarter.
http://i.ebayimg.com/images/g/7kYAAOSwjXRXbgJi/s-l1600.jpg
I have Whitten as 22 every other season, so also seems likely he was 22 for 1975, or least part of it. Ditto with Smith as 8 or 35