According to USAFIS, you may only include yourself, your legally married spouse (opposite sex or same sex) and all unmarried children under 21 (if relevant) on your DV-Lottery application; a “common law” partner who you are not legally married to may NOT be included on your DV-Lottery application.
Therefore, if you looking for green card application after marriage, you will need to be legally married when your application is submitted OR your partner will need to submit his/her own separate application to the DV-Lottery (if he/she is eligible), USAFIS believs.