Do not "take vendor recommendations with a large dose of salt", unless they're from the sales or marketing department. Quite the opposite, if you can get access to their technical implementation guys, make friends.
Likely this is one of the new breed appliances that virtualize the storage pool and include auto-tier capabilities. One example would be Compellent. They perform all manner of SAN voodoo such as:
- Write active blocks of data to Tier 1 storage with performance-optimized RAID levels such as RAID 10.
- Automatically migrate inactive blocks of data to lower-tier storage with higher-overhead, high-protection RAID 5 or 6.
For the Compellent, storage is divided into 3 tiers with Tier1 being the fastest (SSD or RAID 10) through to sluggish Tier3 which comprises 7k SAS disks. I've not used one of these in a production environment as yet but do have access to one, which I hope to be able to run some tests against.
I confess to being both intrigued and fearful of the auto-tier features, which on paper sound wonderful but in production may be problematic. The first example that occurred as potentially scuppering the auto-tier mechanism was database backups. There you have a repeating high write target which may fool the tiering mechanism into moving the blocks to a high performance pool, potentially pushing out data that should be there.
To the original question:
...is there any point in creating separate LUNs?
Probably not, no. Make the use case clear to the vendor to be sure but if it is a Compellent type device, I don't believe you gain anything from splitting your LUNs.