Yes, however spammers are known to operate on very tight margins (they make a few pennies per million users or something) so even slight additional operating costs can seriously affect their bottom line, possibly sending a profitable operation into the red.
So eventually forcing spammers to employ humans instead of bots is not for naught.
It depends on what type of spam we're talking about.
The obvious here is social network spam (you don't enter captchas to send emails), which is where captchas are most used against spammers, can be very profitable ($xxx per x,xxx-xx,xxx users).
So eventually forcing spammers to employ humans instead of bots is not for naught.