I'm certain the engine wasn't stopped when the backup ran. Is that a show stopper?
SQL locks the database files open while it's running. That means that most backup tools will skip the files (they're locked). If you have one of those backup tools that can read locked files then it's a gamble whether those files are usable or not and that's because of the way that SQL writes to the files, they're never guaranteed to be consistent unless the DB is closed, offline, detached or SQL is stopped.
Maybe they'll work, maybe they won't.
File system backups are not a backup strategy.
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
We walk in the dark places no others will enter
We stand on the bridge and no one may pass