Okay we figured it out. Here is the response from Sierra Wireless tech support:
Allow Peer Dynamic IP means that the ALEOS gateway will support changes to the PFSense server IP and doesn’t not have to remain statically configured (ie, 172.22.0.1, 172. 25. 0.2, etc).
Disabling the NAT option means that the private network will not get translated to the ALEOS WAN IP. The source packets will remain as the private LAN IPs even if it traverses the tunnel.
So by disabling the NAT option, I fixed my issue. My source IPs are now unchanged, and SNAT is disabled.