No, the AP2600 series does not support ARP Proxy at all.
On the AP3600 series this was not contained per default in the hardware, so an implementation was coded in a proprietary way
In all Identifi AP series from the AP3700 onwards this feature is included in the hardware.
Based on this, it is not recommended to use ARP proxy in a mixed environment that includes AP3600 series and newer models.
Mixing only newer AP models (AP3700 an onwards) should not be causing any issue with ARP proxy behavior.