I’ve seen a few poker WP themes with sponsored links get penalized in the SERPs – so it can be a grey area and somewhat risky…especially if the theme gains a lot of popularity and gets used on a bunch of sites at once. Google could see it as very spammy if a ton of links just started showing up “unnaturally.”
It seems to work better in some industries than others, and is probably more of a short term strategy. For long term strategy, I would stay away because I think G will ultimately dish out unfavorable results for such tactics.