limitation in the amount of disks presented

I don't believe there is a fixed limit for Volume Manager, but the more LUNs you tadd o a diskgroup, the longer the diskgroup will take to import and deport.  Which disks are in a diskgroup are stored in the private region, so you could run out of private region space, but you can increase the private region space.  

So there are practical limits, but I don't believe there are any theoretical limits.  Usually it is better to have a small amount of large LUNs, rather than a large amount of small LUNs unless you need really high performance by combining hardware striping and s/w striping using VM.

See some other associated links:

https://www-secure.symantec.com/connect/forums/maximum-number-disks-disk-group - this is for Windows, but any limits in Windows are likely the same or higher in UNIX

https://www-secure.symantec.com/connect/forums/multiple-luns-disk-group

Mike

also see duplicate question here:

https://www-secure.symantec.com/connect/forums/dmp

(the OP did create a separate post eventually; in future please refrain from adding unrelated questions to an existing post ie: create the new post correctly in the first place)