Allow AR to use asset custom fields of SNMP devices

I’m trying to setup alerting based on whether a client has after-hours support in their SLA package. I can get AR to trigger an alert only during business hours for Syncro assets by using the Business Hours check and the “Asset Custom Field” check (i’ve got one called “after-hours-support” that gets filled in automatically every week by a script that looks to a custom field of the asset’s Customer - another frustration that I can’t draw direct from customer custom fields in AR). This works, if the field says “No” then the alert isn’t emailed to our alerting system. If “Yes”, then it will.

But I can’t get AR to look at the same custom field of an SNMP device, even if it has the same name, which seems like a big oversight and makes AR only useful for computers. What if I am monitoring something like a UPS, or a NAS? Clients that pay us for after-hours support expect us to fix these too, and they can be just as critical as a server. But we don’t want to get alerted for every customer we have, because our poor on-call tech will have his phone blown up with alerts that aren’t relevant till our office is open again.

Please, can we use logic against SNMP devices’ custom fields as well?