In Tree view doesn't hide complete column when we use attrs="{'invisible':[('partner_name', '!=', 'XYZ')]}", I found it only hides the data/content in that column. So I tried to using invisible="context.get('partner_name') != 'XYZ'" instead of above one. It hides the complete column in Tree view. I hope it will help you.

try to add this code in a new module to install :

python code with new api v8 :

from openerp import models, fileds, api

class SaleOrderLine(models.Model):

    _inherit = 'sale.order.line'

    partner_name = fields.Char(_get_partner_order_name, string="Partner order name")

    @api.one

    @api.depends('order_id', 'order_id.partner_id')

    def _get_partner_order_name(self):

        self.ensure_one()

        self.partner_name = self.order_id.partner_id.name or ''

xml : hide column price_unit

?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record id="view_order_hide_columns_form" model="ir.ui.view">
            <field name="name">sale.order.hide.columns.form</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='order_line']/tree/field[@name='product_id'] position="after">
                    <field name="partner_name" invisible="1"/>
                <xpath expr="//field[@name='order_line']/tree/field[@name='price_unit'] position="attributes">
                    <attribute name="attrs">{'invisible': [('partner_name', '=', 'XYZ')]}</attribute>
                </xpath>

        </record>
    </data>
</openerp>

Bye