Family definitely has to approve, at least after the fact. Ethiopians are very communalistic, and their relations to their families is extremely important. Very like Spain, though Spain has become far more secular and liberal only in the last generation since Franco.
Ethiopian marriages are elaborate, and also diverse in the actual custom, depending upon the tribe (and religion) he is from. Usually, there is a dowry paid from the man's family to the woman's family (in the case of the woman being Ethiopian). The proposal is a socio-political clan-to-clan affair, with the groom's family elders dispatching from the groom's family home (the unmarried man would have usually lived at home until marriage) to the bride's family home to ask formal permission. There is artifice in this, as the elders have done extensive negotiation and planning before the actual proposal ceremony, and there will be food and drink (tej, wine, beer if they are Orthodox and juices if they are Muslim or more abstemious Protestants). Today, urban, educated brides and grooms probably arranged the engagement beforehand between only the two of them, and likely are quietly "dating" (in the Western sense).
The wedding itself is wild and very fun, with food, drink, and group dancing! Many Westerners who marry Ethiopians will have two ceremonies: one in Ethiopia and another back where they are from. Perhaps they will only bring close family from Europe or North America to the Ethiopian ceremony, and usually it would be very costly and difficult (for visa reasons) for Ethiopian relatives to travel to the West (this is very delicate, so be careful not to offend!). The wedding (and dowry) is a HUGE cost for Ethiopian families anyway, and they will often borrow money to pay for it. There might be a caravan of white Mercedes with roses on the hoods and film crews hanging out of windows! Keep in mind that the wedding is mostly for the benefit of the clans and strengthening social relations between families and their status within the community--not the couple themselves.
From a bureaucratic point of view, the challenge will be more on the Spanish side than the Ethiopian side, since the EU authorities are wary of African migrants falsely marrying for residence and citizenship. Note that having dual-citizenship as an Ethiopian is technically not allowed, so, if they do plan on moving permanently to Europe, etc., he would be encouraged to abandon his. In practice, many Ethiopians keep their passports and just don't tell the authorities that they have become a citizen of another state.
Best of luck to your friend!
