Hi Axel,

For external snippet embed in odoo website, you can use iframe:

https://stackoverflow.com/questions/42346566/embed-html-code-inside-odoo-form

There is one app that is used to embed external snippet just try: 

https://apps.odoo.com/apps/modules/9.0/website_embed/

https://apps.openerp.com/apps/modules/10.0/website_event_snippet_calendar/

https://apps.openerp.com/apps/modules/9.0/website_iframe_snippet/

Hope it will useful for you..