Xenserver hotfixes are released as patches that need to be applied with patch-pool-apply. Although technically this could work with XCP as long as you got the correct Xenserver patch it's better to apply patches the "new" way using Yum and the default xcp repository.
Any minor software updates to Xen Cloud Platform will be released into the XCP Yum repository at downloads.xen.org. XCP 1.6 comes with a ready made Yum repository file at /etc/yum.repos.d/xcp.repo although by default the repository is disabled.
To apply updates use the yum update command you have to enable the repo and tell rpm not to gpg check the packages. Hopefully the latter behavior will change in the future.
yum --enablerepo xcp --nogpgcheck update
If you'd like to enable the repo and turn gpg checking off by default so future updates are easier then change the enabled=0 line to enabled=1. Also add a line to the /etc/yum.repos.d/xcp.repo file to turn gpgchecking off for this ONE repository.
[xcp] name=XCP 1.6 Updates baseurl=http://downloads.xen.org/XCP/repo/xcp-1.6.10/ enabled=1 gpgcheck=0
I don't know if I recommend enabling by default as I like to do my updates manually. I really have issues with turning gpg checking off but currently the packages are distributed without a gpg signature so if you have it turned on the update will fail. Our only choice is to turn it off.