You hit the nail right on the head when you said that there are a lot of variables, but the 35mm cannot come close to the digitals when it comes to the number of pictures stored.

So, I guess the issue would be, does a 35mm capture pictures more reliably than a digital? This is where the variables come into play and you need to talk about specific trail cameras.

In my opinion the much larger picture storage capacity of the digitals pretty much rules out the 35mm. The 35mm is limited by the capacity of the roll of film whereas I've had as many as 800 pictures taken by one of my digitals on a 1G memory card.