Well, any exclusion is more or less dangerous (depending on how exactly the mask is set, for example).

However, as far as I know, Avast scanning should be synchronous - i.e. there shouldn’t be any sharing violation, the calling process is simply stopped and waiting for the scanning to finish (unless some strange multi-threaded processing takes place). Can you tell us more about the problem - i.e. what program is that, how to reproduce the issue etc.?
Thanks.