Could be. Voltage supplied by stock power adapter (24V) is fine, PoE out capacity of hAP ax2 is 0.6A which translates to 14.4W. SXT LTE kit uses 5W plus whatever LTE card draws. PoE in will be less than 14.4W, depending on UTP cable length and quality. With cable length not excessively long (e.g. up to 10m) and decent cable quality it should still provide 10W+ on SXT PoE in which means 5W+ available for LTE modem. Which should suffice in most cases.
If that fails, you can still resort to using supplied PoE injector (or
RBGPOE) and 48V 1A power adapter.