Choosing the proper bearings for replacement Hub and wheel bearings: Xero 6902 and 6903 LBLU. I can find 6902 and 6903 bearings, usually 2RS, but I can't find that brand (Xero) and type LBLU (what does it mean?). 

Can I safely replace these bearings with others the same size (6902 and 6903) but different brand and type (2RS instead of LBLU), and expect the same performance and compatibility/suitability, provided they are equivalent in quality? In other words: is any 6902/6903 bearing good enough?

I'm aware that there is a whole science about bearings, with concepts like tolerance and standards like ABEC. It seems to me that bearings for bicycles are usually ABEC 3. But I am afraid that maybe hubs and wheels manufactures choose the bearings that for some reason perfectly fit their components. Or maybe it has nothing to do and all I have to care about is choosing the right measurement. 

This is one of the bearings disassembled, which will not be reused:
Bearings are of standardised dimensions. In your case 6902 is 15 x 28 x 7 (inner diameter x outer diameter x width) and 6903 is 17 x 30 x 7 (which you probably got from Google).

Thus, dimension-wise, as long as you stick to the original dimensions, you're good to go. In other words, you can safely replace these bearings with others of the same size (6902 and 6903) but different brand and type. For the types, those are used in the industry (full source obtained from https://www.astbearings.com/bearing-closures.html):


ZZS - Removable non-contact metal shield retained in the outer ring with a snap wire.
ZZ - Non-removable, non-contact metal shield retained in the outer ring via crimping, or pressing.
2RS - Molded rubber seal. This type of seal is Buna-N bonded to a steel insert.
2RU - Molded rubber seal, non-contact. This type of seal is Buna-N bonded to a steel insert.
2VS - Molded Viton seal. This type of seal is made of Viton bonded to a steel insert.
TTS - Glass reinforced PTFE seal is retained in the outer ring with a snap wire.


You would want to have 2RU or 2RS since they provide the best protection against moisture at the affordable price. The "non-contact" (2RU) means that the seals are not making contact with the inner ring ("shaft" part) - less friction but less protection against dust and moisture.

Concerning the ABEC scale you can read on https://www.astbearings.com/bearing-tolerances-precision-levels.html - there are apparently more parameters than ABEC rating only that determine the longevity of the bearings. Nevertheless, what I've heard from the rollerskates world - not always the higher ABEC class, the better. The bearings rated higher have slightly more resistance but they benefit from less play. Rollerskate riders recommend going not higher than ABEC 5 as going higher introduces too much resistance in rolling.