I can't see why it couldn't be used in a really tight spot, but they are by no means ideal.
I wouldn't go for the single shot type of roman candles, if you can get ones that are like 8 shots of a single colour which may be better for
attracting rescuers.
They are by no means perfect though as they don't gain much hight and the duration of burn is short.
Other uses, I Doubt they have any serious use as weapons unless you really plan on ripping them apart to make some sort of explosive device. However
if your planning on havign enough to make a viable device your going to be carrying alot of fireworks indeed.
Just like everything in survival its about ballancing what you can afford against what you need. I geuss they could be used in a pinch, and maybe they
have other uses like starting fires really fast with wet tinder or something.
I love fireworks so im off to pack some in my survival kit just for teh sake of it