Is the concern teams sandbagging in the playoffs? Should not matter who the kids are playing as long as the kids are the same age group!
Sadly, some teams do bring in other kids from older age groups. Happened to a team we played in a tournament last year. Other team got called out on it and was caught by the tournament director fudging their team roster. They ended up having to forfeit the championship game. Sucks for the kids on the team and the teams they play against.
Random shirt with no name or odd color pants are telltale signs of the non-roster player. You see the cir***stantial evidence every March.
Not all parents pay for matching team gear. Relax most programs are doing the right thing and if this were to happen on my son's team as a parent I wouldn't allow it.