According #1044 partition tables are parsed by erb.

bla<%= @osver -%>blubb
blablubb

bla<%= @host.name -%>blubb

/usr/share/foreman/vendor/gems/safemode-1.0/lib/safemode/jail.rb:17:in `method_missing': undefined method 'name' for Safemode::Jail (NilClass)
/usr/share/foreman/app/controllers/unattended_controller.rb:163:in `load_template_vars'
/usr/share/foreman/lib/foreman/renderer.rb:7:in `render_safe'
/usr/share/foreman/lib/foreman/renderer.rb:45:in `pxe_render'
/usr/share/foreman/app/models/host.rb:225:in `diskLayout'
/usr/share/foreman/app/controllers/unattended_controller.rb:185:in `kickstart_attributes'
(eval):1:in `load_template_vars'
/usr/share/foreman/app/controllers/unattended_controller.rb:163:in `load_template_vars'

bla<% if "bla" == "bla" ->bla< end -%>blubb
blablablubb

It seems to me that partition table is parsed, but the Variables as listed in http://theforeman.org/projects/foreman/wiki/TemplateWriting are not available.