Sentrius RG1xx LoRaWAN Gateway + Wi-Fi / Ethernet + Optional LTE (US Only)

Yes, as long as they are operating on different networks such that AS923 sensors talk to the AS923 gateway and vice versa for AU915 devices. 

No, an RS1xx AS923 sensor will not work with an AU915 gateway because it cannot receive the downlink packets due to differing bandwidth and frequency plans used and therefore will drop off the network.

Once the RM1xx is put into deep sleep, it can wake up by detecting an external GPIO signal. GpioSetFunc can be used to configure which pin to use in order to wake up from deep sleep.

From the definition of GPIOSETFUNC (nSigNum, nFunction, nSubFunc), when the GPIO pin is configured to DIGITAL_IN (nFunction = DIGITAL_IN), nSubFunc parameter's bit 4 and 5 control when it wakes up the radio.

Bits 4, 5

0x10 When in deep sleep mode, awake when this pin is LOW
0x20 When in deep sleep mode, awake when this pin is HIGH
Else No effect in deep sleep mode

For example, the following line of code sets GPIO pin# 28 to trigger waking up RM1xx from deep sleep when it goes from HIGH to LOW. rc = GpioSetFunc(28,0x01,0x23)

Refer to GpioSetFunc defined in RM1xx BLE Central smartBASIC Extensions Guide v1.1 for more details.

End-devices do not actually make a connection with a gateway. End-devices broadcast to all gateways within range and the gateway forward packets to a network server if it can hear them. So, a gateway does not have a hard number for supporting devices and it is rather dependent on how much bandwidth a gateway can support. For example, factors such as payload size, interval of each data transmission or data rate being used can affect how much air time is consumed and therefore the gateway processes. Also environment factors should be considered.   

It's normally best to experiment with real devices in actual sites in order to figure out how many devices can transmit data without much data loss, using desired configuration/setup.

LoRaWAN 1.02 spec requires the end-devices to broadcast JoinReq message on Freq 923.2-923.4 Mhz.  The max output power is 14dBm. The end devices can only use SF10BW125 to join the network, which is DR2.

There are a number of low cost hobbiest gateways on the market based on devices such as the Raspberry Pi, paired with a Semtech SX1272/SX1276, normally used in a LoRaWAN node. These low cost gateways often are single channel devices, operating on a single spreading factor. A single channel gateway can miss many of the LoRaWAN messages broadcast. The Laird RG1xx is an 8 channel gateway based on the industry standard Semtech SX1301/SX1257 chipset providing a scaleable solution able to receive on multiple channels/spreading factors at the same time.