State Equation of negative resistance from current source
No component, when placed in series with an ideal current source, affects the rest of the circuit. This includes positive resistances, nonlinear resistances, voltage sources, inductors, capacitors, or the combination of a negative resistance and a capacitor like you have here. Regardless of what you put in series with it, the ideal current source figures out how to force its designed current through it, so the total source (ideal current source plus series element) is just equivalent to the ideal current source alone.

In the real world, of course there are no truly ideal current sources. But you haven't shared (and maybe don't know) enough about what the actual current source is in your circuit to predict whether the real current source will behave like an ideal source in this circuit or not.