I have used both fluids, without any major problem. I would however not recommend mixing them. I replace my antifreeze every 30000 or 2years religiously. I believe you will find alot of discussion on this board if you do a search. Hopefully it will put your mind at ease.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)