The spacewalk client install needs some workarounds as the arm packages are not available. The advantage is that all but one package are available as architecture independant packages. The workaround is to use the x86_64 client repository and compile the remaining package.
yum install http://yum.spacewalkproject.org/2.5-client/RHEL/7/x86_64/spacewalk-client-repo-2.5-3.el7.noarch.rpm
vi /etc/yum.repos.d/spacewalk-client.repo # change the link to use the x86_64 repository instead of the OS variable
yum install -y rhn-client-tools http://<spacewalk server>/pub/rhn-org-trusted-ssl-cert-1.0-2.noarch.rpm rhncfg-actions rhncfg rhncfg-client http://armv7.dev.centos.org/repodir/c7-pass-1/m2crypto/0.21.1-15.el7/armv7hl/m2crypto-0.21.1-15.el7.armv7hl.rpm
cd /tmp
yumdownloader --source rhnsd
yum install -y gettext
rpmbuild --rebuild rhnsd* # you are not supposed to build this as root... but it works...
yum install -y ~/rpmbuild/RPMS/armv7hl/rhnsd-5*
rhn-actions-control --enable-all # after provisioning install
rhnreg_ks --serverUrl=https://<spacewalk server>/XMLRPC --activationkey=1-centos7-armhfp --sslCACert=/usr/share/rhn/RHN-ORG-TRUSTED-SSL-CERT