Can APE be installed on an HA Standby server (multi subnet)?

At a very high level, You have 2 options as I see it which depend on the reason for needing the APE.

1. Stack the APE license on your existing Orion server which if I understand is already protected with HA. This would increase your polling capacity and both the Orion server and stacked APE would be protected by HA.

support.solarwinds.com/.../Activate-stackable-poller-licenses

2. Deploy the APE and protect it with HA also. This would require a separate HA license.

documentation.solarwinds.com/.../ha_what_is_high_availability.htm

Thanks for the reply. Ideally, I would like to install APE on the HA Standby server, but I asked SW Support and their reply: 
" Unfortunately, this is not possible. A standby server and an APE are two different types of scalability engines and are treated as separate servers in the database. Please see article for more details: https://documentation.solarwinds.com/en/success_center/orionplatform/content/orion_platform_scalability_engine_guidelines.htm"

It would be great to install APE on the HA Standby and wonder if Tony agrees. 

Yes, the support is right.  HA was conceived that if the Main Server goes down, the HA Standby Server will be able to act as the Active Server.

If it will be used as an APE, then it is no longer a Standby Server and would be an Active Server as it actively Polls data from Devices.

Yes, the support is right.  HA was conceived that if the Main Server goes down, the HA Standby Server will be able to act as the Active Server.

If it will be used as an APE, then it is no longer a Standby Server and would be an Active Server as it actively Polls data from Devices.