I would'nt give a game that could not be rendered correctly on a 64x64 display 5 stars for authenticity.
Its not 100% 64x64 then.
However according to the FAQ
"Can I use screen effects like CRT or scanlines that may exceed the actual 64x64 limit? YES! But, make sure it's optional and that the game itself is 64x64 before effects."
So if the bloom is a screen effect and not something thats applied on a per object basis it might be within the rules.
If you're dead set on using them I suggest having them off by default.
Perhaps try getting in touch with one of the hosts on discord.