Gareth, to reiterate what Sanford and Justin have said here, it sounds like the partner you are engaged with is "missing the point" when it comes to how to best leverage Marketo.
I have a lot of experience setting customers up to be successful with Marketo and Sugar in unison - if you'd like to chat directly about it to bring in a "third party voice" to your discussions just let me know - I'm Zak[at]BedrockData.com
And thanks Justin for the Bedrock Data mention, we can help with Marketo-Sugar integrations and increasingly customers are looking for a third party platform to make the connection more robust than the native connector offered by Sugar in the past.
This kind of response from CRM/IT people is not unusual - most of them simply do not understand what a marketing automation platform is for. Having separate databases in 2 systems and trying to keep them sync'd by using rules will only lead to headaches. It would be interesting to understand exactly why your consultants want to keep the records excluded from Marketo; are they worried about cost, syncing overhead (can be mitigated), governance (again can be mitigated by restricting edit/delete privileges to the CRM) ?
One potential route is to explain that Marketo and a CRM are one system in reality, they just do different things with the same data.
Hi Gareth - Were you able to get on the same page with the IT consultants. As an FYI I wrote this today highlighting common scenarios for the Bedrock Data connector for Marketo and SugarCRM.