Create a related field and hide it in the form view, then write it into the attrs attribute of the view definition:

class my_model(osv.osv):
    _name = 'my.model'
    _columns = {
        # ...
        'other_field': fields.related('other_object_id', 'other_object_field', type='boolean', string='Other Field'),
    }

<field name="my_field" attrs="{'required': [('other_field','=',True)]}"/>
<field name="other_field" invisible="1"/>