I had an el-cheapo UPS (beige APC-CS500) for 5 or 6 years working fine with an active PFC Seasonic (s12, 600w). This worked great all that time, though now the UPS battery is finally toast. I intend to just buy a replacement battery for that build.
My new rig sports a Seasonic x750 and I just opted for one of the CyberPower Pure Sine UPSes (810w). Partially due to this debate but I also wanted one with USB control options to shut things down at some point. So an upgrade was inevitable.
To sum up I'm virtually certain your PSU would work just fine with a simulated sine wave (like my old active PFC Seasonic did).... BUT... in the absence of convincing online anecdotes I bought into the marketing / groupthink and went for it anyway for the new rig.
the incompatibility is that switchover to battery may cause an overload on the UPS circuitry due to the APFC circuitry suddenly demanding more current than it normally uses (in-rush current). Kind of like an electric motor using 2-3 times the power to start than it needs while running. This overload normally shuts many UPS's down to protect themselves. The larger the APFC power supply - the bigger the load it can draw during the switchover period.
So you see sometimes its not a problem and sometimes it is. All depends on the actual build. Even APC will tell you this.