According to this site, the 3481 uses the 3270 protocol, which isn't that difficult to parse and process, but definitely not dumb.
I have seen "middleman" applications that allow to use a 3270-type terminal to interact with other applications (e.g. z/OS UNIX) which expect dumb terminals, but usage is quite different from what one is used to. It shouldn't be too hard to write such an application, but definitely time consuming.
More difficult will be the link and physical side: I couldn't find any details about the interface of 3481, but if it uses 3270-style coax, it will probably use IBMs SNA on OSI Level 3 and SDLC on OSI Level 2. Which definitely means soldering and an arduino, and writing a good bit of some kind of network-stack for it.
Physical specs are for example here. There are/were chips (called USART) that act similarly as an UART for the RS232 interface, e.g. the Intel 8251A or Zilog Z85230/Z80230/Z8523L/Z85233, but I think they'll be difficult to obtain.
If you manage to make it work somehow, please keep us informed; I'd be very interested.