During the initial and ongoing sync Marketo will pull in all your SFDC Users.All the SFDC user fields are read only and custom fields are not usable in Marketo. If a user is owns an account or lead/contact, tokens for the owner can be used in emails:
SFDC Owner Related to the Company
{{company.Account Owner Email Address}}
{{company.Account Owner First Name}}
{{company.Account Owner Last Name}}
SFDC Owner Related to the Lead/Contact
{{lead.Lead Owner First Name}}
{{lead.Lead Owner Last Name}}
{{lead.Lead Owner Job Title}}
{{lead.Lead Owner Email Address}}
{{lead.Lead Owner Phone Number}}
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