Does linux/systemd/agetty support doubble ended serial-getty consoles?

My apologies if this is a ultra basic question: Does linux / systemd / agetty support double ended serial-getty consoles? For example I have two remote servers A and B, they are running a recent ubuntu with systemd, agetty and screen installed. There is a null modem cable installed bewteen the servers and it appears on /dev/ttyS0 on both. From Server B I can use screen to get a login prompt (agetty) on server A. From that prompt I can reboot the server A, grub comes up I can make choices in grub, boot Linux, I see the boot messages, then a successful login prompt etc all over a serial link from B. Is it possible to do the reverse with the same serial port/link ? Can I use screen to login to server B from A over the same /dev/ttyS0? Can server B also have agetty listen on /dev/ttyS0 when it is not in use by screen? And if not and I need a second serial port/cable to get from A -> B, is that a hardware limitation of UART or a software limitation of agetty or systemd ? And if its a systemd issue it this possible in a non-systemd Linux say Gentoo? Thank you in advance.