It will work, but there are some risks involved.  Here is a good post on spiceworks where a couple people talk about possible issues. [URL] 
Hi Experts We have PowerEdge 2950 with RAID 5  PERC 6/i Integrated. It has 3 SAS HDDs and it is showing HDD Predictive Failure for two SAS HDDs and each HDD is 400GB. The same size disk is not available now and vendor is asking us to use 450GB HDD. Is it possible or we should insist  on getting 400GB SAS HDD?  Regards      
PowerEdge 2950 HDD Predictive Failure