Yes you can. It is perfectly acceptable (and supported) to install just the kernel part of a rollup, so you can for example have your application version on 5.0.1000.52 (original SP1) or perhaps 5.0.1500.2985 (rollup 5) and have the kernel version on anything above 5.0.1000.52, such as 5.0.1500.3761 (rollup 6), or maybe something even newer!
I will explain the rules very briefly:
- We have two different main levels of release: service packs and hotfixes (rollups are just a group of hotfixes).
- In a service pack release we ARE allowed to have a dependency between the kernel and application builds. This means that you can't mix two different service pack levels or strange things will start to happen in your system.
- In a hotfix release (rollups are just a group of hotfixes) we ARE NOT allowed to have a dependency between the kernel and application builds. This means you can mix any kernel and application hotfix builds - of course you still need to make sure you're not mixing service packs, so as long as the kernel and application builds you're mixing were both designed to go on top of the same service pack then you're ok.
You might also wonder "What is the difference between a service pack and rollup?", some people may have heard that there is no difference - well that is not strictly true. As you can read above, we've explained one difference - in a service pack there can be a dependency between the kernel and application.
There are also other differences - the really big one is that a service pack release effects supportability - so when a new service pack is released, the old service pack has around 24 months before it falls out of support. This means that if we release service packs too fast we can have a negative effects on our customers, pushing them out of support or forcing them to upgrade when they might not be ready, so we take the decision to release another service pack very seriously.
On the other hand, a rollup is just a collection of normal hotfixes put together in one download (and retested together as one) for convenience. This also gives us a good way to enable customers that want to keep up-to-date with all fixes to do that, without effecting supportability for other customers.