A theory can only be corroborated by the evidence when the negation of that evidence would falsify the theory. That is, the evidence must represent a test of the theory, and a test requires the possibility of failure. Tautologies and metaphysical hypotheses, then, are uncorroborable, since they cannot be falsified in principle.
Is Popper’s corroboration merely inductive support in disguise? No.
Consider the sunrise. My evidence of the sunrise each past morning corroborates my hypothesis that the sunrise will occur every morning, because if the sun had not risen on any of these days, then my hypothesis would be falsified. Every morning is a fresh test of my hypothesis. So far it has passed, and each further success corroborates my hypothesis a little more.
However, what about my expectation that the sun will rise tomorrow morning? Is this corroborated by evidence of sunrises in the past? That is, had the sun not risen on any previous day, would it contradict the claim that the sun will rise tomorrow morning? No. Evidence of past sunrises does not corroborate expectations of future sunrises, even though it does corroborate the general hypothesis that the sun will rise every morning.
The confusion stems from a fallacy of decomposition. That is, supposing what is true for the whole (sunrises in general) is true for its constituent parts (particular sunrises). In this case, while a theory may be highly corroborated, it does not follow that its logical consequences are also highly corroborated.
In other words, corroboration is not transmissible from premises to conclusion in a valid argument. In particular, evidence that corroborates a theory doesn’t also corroborate predictions derived from the theory. Corroboration is not ampliative; it’s more like a scorecard. That is, it’s just a measure of past performance and doesn’t entail anything about future success. Popper said this explicitly.