In actual fact, cm for cm, DVCAM recordings hold less video than miniDV as their track pitch is greater. For example, recording as DVCAM on a tape advertised as '60 minute miniDV' will result in about 40 minutes (it's a ratio of 1.5 to 1).
That notwithstanding, miniDV and DVCAM tapes are completely interchangeable so if you can get a 'mini' DVCAM tape that is longer (doing the math) than you can get miniDVs then go ahead. However, DVCAM tapes should be more expensive than miniDV so make sure your maths is good!
Make sure you get the right tape size as well - most of the long DVCAMs advertised are large format and won't fit in most consumer miniDV camcorders. It's not always obvious from web sites which is which - for example a PDVM-40ME is a 'mini' size, the PDVM-64ME is large size.
Jon