Is it permissible to marry a woman who intends to outwardly embrace Islam for the purpose of marriage, given that she is currently married and unable to divorce?

You must stay away from this woman and sever all ties with her definitively because she is a stranger [to you, non-mahram], and it is not permissible to establish any relationship with her. If she embraces Islam and her iddah from her disbelieving husband ends, then it is permissible for you to marry her Islamically. However, if this entails a legal violation that exposes you to severe consequences, then you should refrain from her until the legal procedures for her divorce are finalized. Before her embrace of Islam, there is no need to inquire about her.