I don't know about conversion, but this will have major impact. First, the Nubian kingdoms are likely to remain Christian and not become Muslim. Second, the various Nubian kingdoms and Ethiopia will become part of an enlarged Christendom. They will benefit from increased trade and intellectual exchange.
It is probable that the Nubians and Ethiopians will participate in various ecumenical councils. I think it is doubtful their churches will become subordinate to the Pope, but some kind of relationship will develop.
The biggest change is that Christendom now has access, or possibly even control, of the Red Sea trade to India. Nubia and Ethiopia will probably benefit from some of this.
A potential issue is that with Egypt under control of the Crusaders is what happens if the Mongols arrive on schedule? Egypt was the last major Muslim power after the Mongols destroyed everything else. What impact will this have? Will the Mongols be more inclined to convert to Christianity than Islam? Or will their captive Muslim populations still encourage them to eventually convert so they can rule them better? That process took centuries.
Another thing is that with Crusader Egypt, you now have much more stable Crsudader kingdoms in the Levant. Cilician Armenia likely survives. The east coast of the Mediterranean is likely to remain permanently Christian controlled.