Não consegui encontrar uma maneira de identificar o tipo de um campo em um modelo de django. Minha solução foi criar um filtro simples para acessar os nomes das classes de campo e widget. Eu incluí o código abaixo, caso seja útil para outra pessoa.

Existe uma abordagem melhor?

## agency/tagutils/templatetags/fieldtags.py
###############################################################
from django import template

register = template.Library()

@register.filter(name='field_type')
def field_type(value):
    return value.field.__class__.__name__

@register.filter(name='widget_type')
def widget_type(value):
    return value.field.widget.__class__.__name__


## client/project/settings.py
###############################################################

INSTALLED_APPS = (
    # ...
    'agency.tagutils',
)


## client/project/templates/project/field_snippet.html
###############################################################

{% load fieldtags %}

<div class="field {{ field|field_type }} {{ field|widget_type }} {{ field.name }}">
     {{ field.errors }}
    <div class="form_label">
        {{ field.label_tag }}
    </div>
    <div class="form_field">
    {{ field }}
    </div>
</div>


## sample output html
###############################################################
<div class="field CharField TextInput family_name">    
    <div class="form_label">
        <label for="id_family_name">Family name</label>
    </div>
    <div class="form_field">
    <input id="id_family_name" type="text" name="family_name" maxlength="64" />
    </div>
</div>