I doubt you'll be able to connect keybord (real or virtual) directly to Vita for remote play purposes however if you're specifically after using keyboard with ARR while in remote session on Vita you have 2 options:

- if you play using the remote play locally and are still in reach of your PS4 you can use bluetooth keybord (or USB one as well with extension cable) while in remote play mode
- if you play from remote location / via internet you can you your tablet or mobile phone with playstation app as an external keyboard