How to poll a single device in two different maps

As long as the same probe with the same settings are used, as described in the reference link below, polling will be shared among the devices, and the license device count won't be incremented for the additional device.

About Packet-Based Probes

You can use two probes on one device and use one device license by using probe groups. If the devices are selected and Insert > Group is used (or right-click > Group). The group counts as a single device, regardless of how many members are included.

It is possible to share polling between multiple devices on the same or different maps if the ping/echo or SNMP probes in use match exactly and all the polling parameters do as well.

The settings to check are listed here; About Packet-Based Probes

The other option is to have the multiple device copies on the same map and combine them in a probe group by selecting them and using the right-click "Group" option.

It is also possible to add probes to a device or probe group using the Probes tab in the (right-click) Info window, using the + sign. ref:  Creating Probe Groups