Some of the hot fixes may be available in Windows update if they are a part of a rollup but most are on request only via the kb article. Typically they are latest versions of MS iscsi, mpio etc drivers which have the bug fixes.
We have deployed all the NCM required hot fixes to around 60 Windows servers (2008r2, 2012 and 2012r2) which host sql and a handful of 2008r2 servers that host exchange 2010 without any issues. They seem to be pretty rock solid but as always recommend testing a subset of servers first since all environments are different.
I'm not sure of the impact of not installing specific hot fixes but some symptoms I've seen previously are long delays logging into Windows with a black screen, iscsi control panel hanging, clusters losing iscsi sessions and persisting in a reconnecting state and mpio misbehaving.
We've gone through a few Nimble OS and NPM/NCM updates and I have enough confidence now to install them in one hit followed by a reboot (pre prod first, then DR and finally prod). Not one issue so far.
Hope that helps...