Is there a way to sync custom fields which are created under the Campaign Member object in SFDC to Marketo?
Unfortunately you can't do that out of the box with Marketo.
What specifically are you trying to accomplish? There might be a workaround.
In SFDC, we tag contacts with campaign members
Let's say in the Campaign Member object, a custom field as "Relationship Owner"
So if there is a Campaign named "XYZ campaign", we tag 10 contacts with XYZ campaign.
Among the 10 contacts, 4 contacts have relationship owner as Mr YY, and another 6 have the relationship owner as Mr ZZ.
So for the first 4 mentioned contacts, we associate XYZ campaign and select Mr YY as a relationship owner in the campaign member. As for the the rest of 6 contacts, we will associate them with XYZ campaign and select the relationship owner as Mr ZZ
If the Relationship Owner can be synced to Marketo, when in Marketo, we want to be able to Filter Campaign as "XYZ Campaign" and Relationship Owner who is "Mr YY".
Please assist how can we achieve it if there is a workaround.
This sounds more like an Opportunity + Opportunity Role pattern to me... IMO a (mild) misuse of the Campaign Member concept.
In any case you should be able filter on this field, though you can't trigger on it. Look in the Add Constraint list for Member of SFDC Campaign.
I tried but I don't see the custom field of the Campaign Member "Relationship Owner" is available under the Add Constraint?
Could you please assist further more?
I would use a custom object in SFDC rather than a campaign. The reason is that for custom objects, you can have all fields to sync with Marketo, not simply the standard ones.
Anyway, whatever solution you choose, you will have to use some formula fields to bring back the relatioship owner first and last name, otherwise you will only get and SFDC ID.
Can you please explain why the relationship owner is set at the campaign level ? This implies that a contact can be a member of multiple campaigns and have a different relationship owner every time. Is this the real need you have ? If this is not the case, and a contact should have a unique relationship owner at any point in time, why not using the contact owner instead ?
If the multiple contact owner is needed, why are you using the campaign object, which is supposed to help you manage the campaign flow (with member statuses), targeting (through all the features available to add members) and reporting? If these campaign features are not needed, then a custom object would do a better job.
At the end of the day, it's not just about knowing what you can sync with each object, but what are the business needs behind all this.