For the SharePoint Plus library, to set a person field must be provided as "-1;#email" (e.g. "-1;#foo@bar.com") OR NT login with double \ (eg "-1;#europe\foo_bar") OR the user ID as a number.
You can check the source code of the SharePoint Plus library.
/** @name $SP().list.add
@function
@description Add items into a Sharepoint List
note: A Date must be provided as "YYYY-MM-DD" (only date comparison) or "YYYY-MM-DD hh:mm:ss" (date AND time comparison), or you can use $SP().toSPDate(new Date())
note: A person must be provided as "-1;#email" (e.g. "-1;#foo@bar.com") OR NT login with double \ (eg "-1;#europe\\foo_bar") OR the user ID as a number
note SP2013: If "-1;#" doesn't work on Sharepoint 2013, then try with "i:0#.w|" (e.g. "i:0#.w|europe\\foo_bar") ("i:0#.w|" may vary based on your authentification system -- see https://social.technet.microsoft.com/wiki/contents/articles/13921.sharepoint-20102013-claims-encoding.aspx)
note: A lookup value must be provided as "X;#value", with X the ID of the value from the lookup list.
--> it should also be possible to not pass the value but only the ID, e.g.: "X;#" or the ID as a number without anything else
note: A URL field must be provided as "http://www.website.com, Name"
note: A multiple selection must be provided as ";#choice 1;#choice 2;#", or just pass an array as the value and it will do the trick
note: A multiple selection of Lookup must be provided as ";#X;#Choice 1;#Y;#Choice 2;#" (with X the ID for "Choice 1", and "Y" for "Choice 2")
--> it should also be possible to not pass the values but only the ID, e.g.: ";#X;#;#Y;#;#"
note: A Yes/No checkbox must be provided as "1" (for TRUE) or "0" (for "False")
note: A Term / Taxonomy / Managed Metadata field must be provided as "0;#|UniqueIdentifier" for the special hidden related column (see https://github.com/Aymkdn/SharepointPlus/wiki/ to know more)
note: You cannot change the Approval Status when adding, you need to use the $SP().moderate function
*/
Source code: sharepointplus-5.2.js