Enabling ELM for local mode APs(AP mode: Local, AP Sub mode: wIPS) is often practiced with no issues ever faced.
I have a deployment requirement to enable ELM mode on flexconnect APs. This is however possible as part of Flexconnect matrix, however would want to make sure if there are any specific limitation/ consideration that I need to take into account for this
It will send more control data over the WAN Link but that should be it.
The AP will report the information to the WLC and the AP mode (Flex or Local) is irrelevant for the AP ELM Functionality. Just keep in mind that it will add more CAPWAP control traffic, which may only have an impact if you're using a very low bandwidth link. However, it shouldn't be a problem.