There's only a need to donate if your hematocrit or RBC's are high, or maybe even if they're trending upward. Other than that, just donate because you'll be providing a valuable service to patients who are in need.
There's no need to cycle off the hCG unless that's your preference. There are some people who feel that it should be done to prevent desensitization of the Leydig cells in the testes, but there really isn't much research backing up those claims. Many guys who say this are merely repeating something they read on an Internet forum.
Maybe it's a possibility, maybe it isn't, I don't know. But I wouldn't be too concerned about it until there is some factual information to go on.
It would make sense that problems may arise when very high doses of hCG are used but at the small/moderate doses used with TRT, I doubt there is much concern at all.
I mean, why wouldn't I want to keep my testes functioning normally?!