As others have pointed out, there are multiple views within Christianity on almost everything. But a lot of those views are somewhat marginal; there’s what we might call a broad consensus among mainstream Christian denominations on a range of issues. Relevant to the OP, I think this consensus would include:
- There’s no doctrinal position that there are, or that there are not, intelligent races elswhere in the universe. You can think what you like about this question; it doesn’t impair your identity as a Christian.
- The Incarnation is a unique event; God does not become incarnate separately at different times and different places. However you probably could postulate a unique incarnation that is manifested at different places in the universe and/or at different times. It’s speculative, obviously.
- The sacrifice of Christ is for the redemption of the whole of creation. Therefore, if there are intelligent races elsewhere in need of recemption they don’t require a separate sacrifice to be redeemed.
Somewhat analgous questions arose a bit over 500 years ago, when Christians discovered a hitherto unsuspected New World, filled with people who were wholly unaware of the claims of Christianity. Could they, and the many generations of their ancestors who had died before ever hearing of Christ, be saved? The Europeans who discovered and colonised the New World were overwhelmingly Catholics, and the position they arrived at was (1) it was important and necessary to evangelise the New World, but (2)_God certainly can save people who die without ever being evangelised; individual faith in Christ is the only assured route to salvation that we know of, but God cannot be limited by what we know. And that’s still the Catholic view.
Subsequently, along came the Protestant reformation, and a greater diversity of theological views among Christians, and then subsequently again along came what you might call the insistence on a simplistically literal reading of scripture, and then along came American Evangilism and the stress on accepting Jesus as your personal saviour, and a generally very individualistic approach. So probably there now would be a non-trivial chunk of Christians who would argue that pre-Columbian Americans must be considered not saved, because they could have heard and responded to the Gospel.
You can see how this could map on to the discovery of intelligent alien life. The consensus would probably be that, if they are sufficiently like us to make salvation a meaninful concept, they could be saved. Nobody would argue that that would require a separate incarnation or a second sacrifice of Christ. But opinon would be split on whether they could only be saved if successfully evangelised, and brought to personal faith in Jesus.