svnadmin hotcopy will always create full copies of your repository. It is not possible to do incremental backups with svnadmin hotcopy.
svnadmin hotcopy works like a filesystem copy command, except it will never copy open transactions.
To restore a repository you can just svn hotcopy your backup to the place from which you want to serve it.
For checking the integrity of a repository use svnadmin verify
eg:
assume your svn repos are on /var/svn/repos and your backups are stored on /var/backups/svn and your repository my_project is broken.
Use:
svnadmin hotcopy /var/svn/repos/my_project /var/backups/svn/
to create a new backup (do this every day or week..) and:
svnadmin hotcopy /var/backups/svn/my_project /var/svn/repos/
to restore your backup (note: you have to remove your repo before, as hotcopy will not overwrite your old repo, also you really should look for the cause of your repository failure).
Also use:
svnadmin verify /var/svn/repos/my_project
for checking the integrity of your repository