have a customer that is running Horizon 7.5 Standard with windows desktops. they also purchased 50 licenses for Horizon for Linux Standalone. Is there anyway to use the Linux license with the existing Connection server? or does it need it's own separate environment. can't add both keys. i've looked everywhere and can't find anything that says one way or the other.
No, there is not way to do that. That is why Linux also comes in Enterprise edition of Horizon View.
If you want to have all the features in one platform you will need that edition. If you see this datasheet i am sure your issue will be clarified https://www.vmware.com/files/es/pdf/products/horizon/vmware-horizon-7-faq.pdf