Is there evidence of differences in the outcomes of objects-early vs objects-late?
tl;dr/ Students tend to do what they have the most practice doing. But timed contests can advantage/disadvantage some students independent of skill and background. 

I have to admit I'm not a big fan of timed contests for programming. I don't know if that is the situation here, of course. The problem is that they favor quick thinking over deep thinking. If you don't have time to get something for every question your score likely suffers even if your solutions to the ones you work on are brilliant. 

My advice to a student taking such a challenge would be to get something for every question. 

That said, I would expect that students who have seen a lot of OO, and, in particular, have written a lot of classes themselves would naturally (and quickly) put down a class framework and then write methods. Less likely (given time constraints) would they do a problem decomposition into appropriate helper objects and composition of objects to solve any problem. It just takes too long, unless they have an IDE that will produce class/method templates at a click, or use JUnit or similar to build the application scaffolding for a given test. 

Likewise, I'd expect that a student with little experience in creating classes would be more likely to just write functions, even if they had seen objects/classes. In a way, assuming that the test judging criteria allow either approach, these students may have a bit of a time advantage since there is less to type. 

The psychological effect here is that you tend to do what you have the most practice doing. So Object-Early students automatically start by writing class ..... and Object-Late students may not. But there is little time for reflection on the quality of your overall structure in any case. And likely none for refactoring. 

A possible countering psychological effect, since the competitions/challenges take place during the school year is that there is a tendency to repeat what you have most recently been focused on, being fresh in your mind, though less settled. 

My bottom line, however is that programming isn't best tested in a timed environment, especially when the questions can be tricky in some sense, where you get an advantage, perhaps serendipitously, if you just think of the trick involved or have seen it before. Some students (my history says I'm one of them) is disadvantaged in this situation. 

On the other hand, I can write code very quickly (hundreds of correct lines of code per day) with good tools and practices, including test-driven development with a good IDE (Eclipse). But if you give me a variation of NIM or some other mathematical puzzle, I'll stare at it for too long. 



I also teach objects from the start (before if and while) since I value large scale structure over small. That is, providing a solid framework for the smaller scale issues.