This is possible.

Nothing prevents you from either passing some instance $x of class X as an argument when tying a scalar to class Y, or tying a hash that contains a reference to $x. You can still hold on to $x, as can the tied scalar. It's up to you, though to ensure that $x's state remains valid if it is access both directly and through the tie API, and are side-effecting $x through both.

It doesn't matter at all whether Y is a submodule of X.