No problem so far...
I usually point slapt-get to slacky.eu (GohanZ) and didn't had any trouble yet.
Didn't runa a production server either yet.
Only breach ever I had on webmin and it's 10000 port
- mine fault and mine alone.
However, I configure my slapt-get rc file by hand and point it only to:
A slackware mirror for patches
I comment out all else.