Nah -- "marketeer" is a modern formulation, but the basic form of "X-eer" has been in use for a long time now. Some examples:

Mountaineer: first use 1600s (http://www.etymonline.com/index.php?term=mountaineer&allowed...)

Pamphleteer: first use 1640s (http://www.etymonline.com/index.php?term=pamphleteer&allowed...)

Auctioneer: first use 1708 (http://www.etymonline.com/index.php?term=auctioneer&allowed_...)

Profiteer: first use 1910-1915 (http://dictionary.reference.com/browse/profiteer)

There are even earlier examples in English (pioneer and charioteer, for instance), but those didn't come from adding "-eer" to an activity; they were loanwords (http://en.wikipedia.org/wiki/Loanword) from other languages, like Old French, which used "-ier", "-eur" and "-aire" the way we use "-eer" today. (So charioteer, for instance, started out as charioteur.) Once the words were adopted by English, the spelling migrated to the form we know today.