I thought I had heard the EtherWave was incompatible with Open Transport and required Classic Networking. But I don't have one, and don't have any firsthand knowledge.
If it requires OT, it will work with OS 7.5 and up, as long as you install the OT software, available on Apple's website.
If it only works with Classic Networking, it may very well work with System 6, but is assured to work fine in System 7. The best thing to do would simply be to test it in the OS you want to use it under. Just because the company has not tested and does not certify it for use with a particular system version doesn't mean it won't work.
If it requires OT, it will work with OS 7.5 and up, as long as you install the OT software, available on Apple's website.
If it only works with Classic Networking, it may very well work with System 6, but is assured to work fine in System 7. The best thing to do would simply be to test it in the OS you want to use it under. Just because the company has not tested and does not certify it for use with a particular system version doesn't mean it won't work.