Not directly, at least not at the moment. Here are the things we support right now, directly through our API:
- Populating a Marketo only custom object related to the person (Soap API)
- Populating account fields on the person (but not linking them together in a full, normalized account and person table structure) (Soap & REST APIs)
In the near term we'll be adding REST support for the custom object and after than adding a set of calls to really create accounts.
Now, if I were you and trying to do this right now I'd denormalize the field and write to that via the API. So, create a field on the person and update every person in that account when it changes. Similarly, you could create a custom object and replicate it across all the people in the account. Not perfect, but I've certainly seen many customers do it.