Должен работать с двойными кавычками, например
smbclient //10.10.101.29/it -W WORKGROUP -U user --password pass -c "put file_$(date +%Y_%m_%d).file"
или
date=$(date +%Y_%m_%d)
smbclient //10.10.101.29/it -W WORKGROUP -U user --password pass -c "put file_${date}.file"