I'm not aware of any such limitation on Android. And if there were, why would UnionPay take the time to develop an NFC payment option on their Android app?
Do you have a link to any UnionPay web page advertising this feature? The only link I can find is one that simply describes how to use the manufacturer's own NFC pay product:
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IOW to use NFC pay your phone manufacturer (Google Pay doesn't work for obvious reasons) must provide their own NFC pay product.