The thing is that this evolves with time. Back in 2000 nobody would have called SnmpUtilOidToA with a NULL parameter as it would have meant crashing on a lot of the Windows install base. Nowadays every ISV expects you to have at least Windows XP and wouldn't care one bit if that call means crashing the application on NT4 or lower.
So you could say that nowadays applications are likely to expect SnmpUtilOidToA(NULL) not to crash which means keeping these tests. However I don't think our conformance tests should crash on older systems and that's what makes things tricky...
I agree with you that resolving issues like this can be subtle, since there will always be specific examples when a general principle does not apply. They don't invalidate the general principle unless they outnumber it or outweigh it in some way. So, in my opinion, the general principle is this: if the behavior is very different on different Windows versions, and if the behavior on some Windows version is to crash, it seems reasonable to remove the test, as: 1) we want our tests to reflect Windows behavior that applications count on, and different behavior (especially crashing) often implies the applications don't count on a particular behavior, and 2) having regression tests crash is undesirable, as many other valid tests will not be run on a platform.
This doesn't mean that we can't make Wine not crash given the bogus input, it just means we may not be able to have a regression test for this behavior. And, of course, there may be specific instances in which we wish to test potentially crashy behavior, but I'd argue that they better be really important to override points 1) and 2).
And coming back to this test: I still think it's easier just to remove the test than to come up with a hacky way of avoiding it on a crashy system. --Juan