If she/he follows 4 regulative principles and chant 16 rounds as prescribed in ISKCON then go ahead with this relation. Of course check other things like horoscope matching etc.
To marry a non vaisnav is definitely bad as it will not allow you to follow 4 regs and then gradually no chanting and gradually all bhakti will be gone. Any thing we do should be for pleasure of guru and Krishna. So if marriage does not help me in getting more KC then what is the use of that kind of marriage.
YS, dev