Yes, you can do it. For that purpose can be used p:column
with attribute colspan
. Following is example how to use it:
<p:dataTable id="tliTable"
value="#{chTransactionsForm.tliList}" var="tli"
resizableColumns="true"
style="width: 930px; margin: 5px 5px 5px 5px;">
<f:facet name="header">
<h:outputText value="#{msg.txnLineItems}" />
</f:facet>
<p:columnGroup type="header">
<p:row>
<p:column rowspan="2" headerText="#{msg.item}" />
<p:column rowspan="2" headerText="#{msg.nacs}" />
<p:column rowspan="2" headerText="#{msg.department}" />
<p:column rowspan="2">
<f:facet name="header">
<h:outputText value="#{msg.purchaseAmount}"
escape="false" style="white-space: pre-line;" />
</f:facet>
</p:column>
<p:column rowspan="2" headerText="#{msg.quantity}" />
<p:column colspan="5" headerText="#{msg.promotions}" />
</p:row>
<p:row>
<p:column>
<f:facet name="header">
<h:outputText value="#{msg.promoName}"
escape="false" style="white-space: pre-line;" />
</f:facet>
</p:column>
<p:column>
<f:facet name="header">
<h:outputText value="#{msg.promoCode}"
escape="false" style="white-space: pre-line;" />
</f:facet>
</p:column>
<p:column>
<f:facet name="header">
<h:outputText value="#{msg.promoCat}"
escape="false" style="white-space: pre-line;" />
</f:facet>
</p:column>
<p:column headerText="#{msg.discount}" />
<p:column headerText="#{msg.points}" />
</p:row>
</p:columnGroup>
<p:column>
<h:outputText id="tliProduct" value="#{tli.productName}" />
</p:column>
<p:column>
<h:outputText id="tliNacs" value="#{tli.nacsName}" />
</p:column>
<p:column>
<h:outputText id="tliDepartment" value="#{tli.departmentName}" />
<p:tooltip for="tliDepartment" trackMouse="true">
<h:outputText value="#{tli.departmentCode}:#{tli.departmentName eq tli.departmentCode ? '' : tli.departmentName}" />
</p:tooltip>
</p:column>
<p:column>
<h:outputText value="$" />
<h:outputText value="#{tli.amount}">
<f:convertNumber pattern="#,##0.00" />
</h:outputText>
</p:column>
<p:column>
<h:outputText value="#{tli.quantity}" />
</p:column>
<p:column colspan="5">
...
Or even more reliable source - Column Group in PrimeFaces showcase