An important point for the answer to this question - the entity governing the Russian America was the Russian American Company (RAC), not the actual government structures of Russian Empire.
The act legalising distinction of creoles from Russians was passed in 1821, and the aim of that act was to increase the population of lands controlled by RAC - Russian workers had to return to Russia when their passports ran out, but their children (according to this act) had to work for the Company for at least 10 years before gaining freedom of movement. In exchange, they were given several privileges.
The RAC effectvely was a "state-within-a-state" with only three "estates" - the workers, the creoles, and the aleutes. These estates were simply social constructs - there are records of aleutes being recategorized as creoles and creoles becoming common Russian sitizens due to promotion within the Company. But this estate structure was limited strictly to territories under RAC control and had no relation to official national politics of Russian Empire.
In Russia proper, on the other hand, children of mixed marriages had nationality of the father, and their mixedness had no effect on their rights whatsoever. Nationality in imperial law mattered little - the only distinction was made between normal sitizens and "inorodtsy" (note that usage of this word was different in legalese and in common speech: former only applied this term to several explicitly named peoples, but in latter it meant "anyone who isn't Russian") - peoples who needed special arrangements for their traditional way of life, like steppe nomads: they were given special lands protected from settlement by other peoples and some self-rule by their traditional leaders, but also paid some taxes not levied from common citizens, for example. Non-Russians not classified as "inorodtsy" (and not a part of a group regulated by other special legislation, like Jews), like Germans, Lithuanians and other European nations, had the same legal standing as Russians.
1) Тихменев П. А. "Историческое обозрение образования Российско-Американской компании и действий ее до настоящего времени"// Москва, Рипол Классик, 2014
2) Николай Вахтин, Евгений Головко, Петер Швайтцер "Русские старожилы Сибири: Социальные и символические аспекты самосознания"// Москва, Новое издательство, 2004