My team used to do similar things. It was never planned, it was more like the guy who talked about the naked mile.
On my team, no one would give you more than a light razzing for not wanting to participate, or if you wanted to participate in a pair of shorts, that would be cool too. As far as getting in trouble, it really depends on the culture of your school. I know at mine, it would have been a matter of campus safety telling us to go home. At some schools though, the actual police could get involved and that would be bad news.
If you think the backlash from teammates would be serious or if they ostracize you for it, then it is certainly hazing. If its just a for fun thing then by definition it's probably hazing, but what the heck, who doesn't like skinny dipping and streaking every once in a while?