As a general rule Juniper will only support optics and breakout cables that they sell re-branded on their name. And the copper breakouts are rare this way.
But I've had good experiences using 3rd party optics and breakout cables. You just need to rely on the 3rd party support then when there are potiential optic issues.
Fortunately JTAC does not shut cases down just because 3rd party optics are installed as some other vendors do. But if the issue is potentially optic related it can be difficult to track down the problem. and good support from your 3rd party optic vendor is a must.
But working with an optic specialist has its rewards in both a wider array of options and potential cost savings.