Well it's a balance, certainly there are very real scenarios from the past 20-30 years where there have been issues with a whole model, line or batch of disks that has meant one disk's failure was likely to be followed by another within quite short time scales and this should be a worry (especially in R5 configurations). At the same time if you're buying from one of the big players then there's a reasonable chance that they wouldn't support anything but their own supplied disks in a given machine, so swapping out some of the disks in that scenario brings with it its' own concern.
If you're building your own servers then obviously this isn't such an issue and it's not even that hard these days to find two disks from different manufacturers that have surprisingly similar performance characteristics - making this route less fraught.
I think a pragmatic approach when buying from the big players is to stick to as small a set of disk part numbers as possible across all of your machines and have a good amount of spares on site, decent support contracts in place and focus on your backup systems. We've done this by standardising on dual 147GB 10krpm 2.5 SAS disks for boot purposes - most of our systems don't need this much boot space but as >99% of our machine use them it's easy to have a big pile of them to hand.
Hope this helps.