An unstable PA design is not ideal and may require additional efforts to achieve stability. It is crucial to address the stability issues before considering the implementation of the design in practical applications.
However, if you have already made a design, you can post this question along with your design here:
If the PA is Conditional Stable, it might oscillate or NOT
If the PA is Unconditional Unstable, it will definitely oscillate.
PAs are designed as unconditional stable as much as possible but conditional stability can be an option with danger of oscillation.
To answer exactly to your question: NO is not okay to have an unstable PA.
Actually, is not okay to have any RF stage unstable, whatever is an LNA, Mixer, IF amplifier, demodulator/modulator, and even an oscillator. Yes an oscillator, which should have a controlled (in)stability (positive feedback), otherwise will have poor characteristics in terms of: frequency stability, phase noise, or start-up.