What is the glaze on a bakery-style fruit tart?
The glaze on most fruit tarts is just melted jelly.  Given the small quantity involved, you probably wouldn't particularly notice the apple flavour.  However, there's no reason you couldn't use another type of jelly if you preferred.

If you take a look at many fruit juice blends, you'll note that the base is usually apple, even when that's not the advertised fruit flavour, so it's obviously not an overpowering flavour when mixed with other fruits.

This Tips for Pies and Tarts page has a couple suggestions at the end for glazes for fruit pies and tarts.