Depends on the song, to be honest. Some tracks have a lot of content ID protection (particularly a song owned by Sony Records, Universal Media Group, or Warner Bros. Records) and even the acapella will get you hit, whereas others you could use whole sections of the track in your own song and be totally fine.
If you're doing an official remix or a song from a remix competition, chances are it won't happen (tho it did for my Mosh Pit remix so YMMV) but if you're doing a bootleg (the proper term for "a remix that i don't have permission from the artist to make") take some time to create a second soundcloud account for it and just repost.