Would the CHECKSUMOFFLOAD setting in the TCP.IP profile dataset affect XCOM in any way?
The creation and verification of the various checksums (IP, TCP and so on) which are defined by the involved protocols (like TCP and IP) is the responsibility of the TCP/IP stack itself. Clients of the TCP/IP stack like XCOM are not even aware of these checksums.
(NO)CHECKSUMOFFLOAD directs the TCP/IP stack to offload checksum processing to the network adapter (when it is able to do so) or to process the checksum via software routines.
Whatever way the stack processes them, it is transparent to XCOM