It Obito were to transport the 2ed or 4th hokage to the other dimension with his kamui, would they be able to use the raijin to teleport out of it?
Minato not wanting to get warped by Obito right before Minato dies suggests that he would not be able to teleport out of the kamui dimension. This is likely because the chakra link needs to be in the same dimension the user of ftg is currently in.
For example kunai is in earth dimension. Minato is in Earth dimension. Minato warps to kunai.
If Kunai is in kamui dimension. Minato is in Earth dimesnion. Minato can't warp to Kunai because the chakra link can't transcend dimensions.
FTG may also have a distance restriction and kamui dimension, being another dimension, is simply too far for ftg to travel to.