Hi!
Yes, it´s a bit dangerous. You should remember it´s a third world country and we have lots of poor people.
Salvador can be dangerous, so can Sao Paulo, Rio and any other city.
But you will survive.
You just have to keep your eyes open, be aware, not walk around showing your camera and your wallet, hide you money (do not take lots of it with you when you go out) and you´ll be OK.
I´m brazilian, I live in a much smaller city, known to be safe, and I´ve been robbed a few times.
Some people I know have lived in Salvador their whole lives and/or been there for carnival and nothing ever happened to them.
There carnival parade is not in a special place as in Rio, but in the streets.
Thousands and thousands of people dancing after "trio elétricos" (a truck with a band playing live on top of it).
To participate in a "bloco" (as they call the different carnival groups), you will have to buy an "abada", the costume they wear for the parade.
I think it´s quite an experience, lots of music, dance, party, happy people.
Not something for me, sweating in the middle of the crowd, but people love it. I´ve never been there, but we see it on TV and some of my friends have been there.
As for safety, I think you don´t have to worry so much.
Just keep your eyes open, get some info from a tourist info office when you arrive, and you can enjoy carnival.
Good luck!