UEMCLI is for VNXe and Unity

for VNX - did you try a knowledgebase search ?

Q1.  Can I use UEMCLI to run against VNX1/2 series storage arrays or is this CLI tool limited to Unity/VNXe systems only?

No, as already answered.

Q2.  In UEMCLI, there is an option when creating CIFS shares, to specify a parameter called OfflineAvailability.  What equivalent would there be in VNX1/2 CIFS shares?

This is SMB3 features and latest vnx 1/2 code supports   (man server_export : Check syntax for OCVDO/OCNone where OC=Offline Cache)