You can of course connect HBAs to two different storage systems from different vendors.
From my experience, what will cause trouble, however, is if you're using management tools, snapshot integration drivers (VSS) or host settings tools from both vendors, as these will generally overwrite each other's settings and get confused easily. for example, SnapDrive might try to snapshot LUNs on 3rd party LUNs and report strange errors.
If you're just connecting these storages for data migration purposes, or are not using any integration tools, you should be fine though.
-Michael