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:
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.