I managed to figure out what i had wrong in the business rule i needed to do 2 selects one to get the value from the request template and 1 to select the records to update.
Updated XML below.
<perform_batch>
<hierarchy_select result_name="ReqTemplateQuery01" max_rows="1">
<primary_table>request</primary_table>
<attrs>
<attr>request_template.user_def8</attr>
</attrs>
<from>
<table>request_template</table>
</from>
<where>
<data_constraint>
<constraint>
<left_operand>request.eco_id</left_operand>
<operator>eq</operator>
<right_operand>@foreign_key_char1</right_operand>
</constraint>
</data_constraint>
<join_constraint>
<constraint>
<left_operand>request_template.request_template_id</left_operand>
<operator>equi</operator>
<right_operand>request.request_template_id</right_operand>
</constraint>
</join_constraint>
</where>
</hierarchy_select>
<mass_update_request>
<hierarchy_select>
<primary_table>request</primary_table>
<attrs>
<attr>request.user_def8</attr>
<attr>request.eco_id</attr>
<attr>request.request_id</attr>
</attrs>
<from>
<table>request</table>
</from>
<where>
<data_constraint>
<constraint>
<left_operand>request.eco_id</left_operand>
<operator>eq</operator>
<right_operand>@foreign_key_char1</right_operand>
</constraint>
</data_constraint>
</where>
</hierarchy_select>
<request>
<user_def8 xpath_node="//request_hierarchy_select_result[@result_name='ReqTemplateQuery01']/request/request_template/user_def8" />
<update />
</request>
<transaction_size>100</transaction_size>
<synchronous>Y</synchronous>
</mass_update_request>
</perform_batch>