I'm using an UISlider for selecting different variants (fragrances to give you an idea) from a group of 12. The slider is about half a screen wide (on iPhone). Comparing to choosing a continuous value when precision is not so important, I imagine users may have difficulty with choosing a specific variant. I chose the slider because it is more uniform and also because the picker would take too much space. Could it be a reason of rejection of an app from apple store? (I haven't submitted yet.)
Almost certainly okay. Is the selection discrete or continuous? A set of discrete choices along a continuum could be a great application of a slider, with a couple caveats:
1) If the choices are really discrete, adjust the slide position after a drag to the nearest choice - like paging in a scroll view.
2) The blue fill on the left side represents an increasing quantity. Does your model have one? e.g. Let's say there are four beverage sizes on the menu, and the discrete positions represent a size the customer can order, smallest to largest. The blue bar here tells you how much beverage is going to be in the cup (even cooler if you rotate it 90 degrees to fill up towards y==0). But how about selecting a season: (spring summer fall winter)? There's certainly a discrete choice on a continuum, but what does the blue fill mean? Days of the year? Not really.
In the seasonal selection instance, I'd be tempted to write my own slider, just like Apple's but with no blue fill. Then again, once you've decided to custom build, you can be less influenced by the standard control.
Here's my anecdotal do and don't list for Apple approval (mostly don't): don't crash, don't call private apis, don't do demo + up-sell, don't copyright infringe, don't interfere with apple business objectives - like sell add-on content outside of the store, do something cool and simple.
But minor slider abuse isn't on my list. Good luck.