Configuring Digi Portserver Serial Thin Clients

I am migrating from SCO OSR6 to RHEL 7.3, and that includes about 20 Digi Portserver TS16's with hundreds of serial thin clients. These were traditionally defined in /etc/inittab in SCO, but I see now that in RHEL 7.3, /etc/inittab has been deprecated.

I have reviewed this knowledge base document, https://access.redhat.com/articles/7212 , but i do not feel it is completely clear how to define ttya01 - ttya16 as serial terminals in /etc/default/grub without trying to mirror the console to each.

Thank you very much, in advance.