I think your sentence is grammatically sound, although we might prefer alterum to aliud and in qua to qua.
Stylistically, there's a lot to consider. In what follows, I'm going to write in a somewhat stream-of-consciousness manner, showing how I might work through the task of translation.
First, I take stock of the basic structure of the English expression: [verbal noun] is [verbal noun]. This is certainly grammatically possible in Latin, but I think it's more usual to have these expressed as some kind of verbal clause, using infinitives or participles. So, I'm going to rephrase this in my mind as something more like "To have gotten married a second time is for hope to have triumphed over experienced."
I think this makes particularly good sense with matrimonium, which is not used very often as a noun outside some kind of verbal construction. We do want one of the relatively few intransitive constructions. I think in matrimonium iterum isse is a good start.
If we're trying to keep the structure [x] is [y], we need esse.
Then "hope to have triumphed over experience" may be best transformed into a passive, so the semantic roles are clear: "experience to have been triumphed over by hope": peritiam a spe vinci.
Altogether, we have:
Oscar(ius) dixit in matrimonium iterum isse esse peritiam a spe victam esse.
Now, to me that reads kind of clunky. Lots of infinitives. Maybe we eliminate one and allow some semantic ambiguity. We could convert the second half into a participle phrase: spem peritiam vincentem.
Oscar(ius) dixit in matrimonium iterum isse esse spem peritiam vincentem.
Alternatively, we could move away from the x is y structure and the ugly connecting esse. While we're at it, maybe we can remove the infinitive from the first half by converting it into a gerund: "in the case of entering marriage a second time..."
Oscar(ius) dixit in eundo iterum in matrimonium, peritiam a spe victam esse.
Maybe a relative clause is cleaner:
Oscar(ius) dixit ei, qui in matrimonium iterum ierit, peritiam a spe victam esse.
Here are some options I came up with. Surely there are many more ways of approaching the issue.