There is nothing wrong with accepting poker sites, as there is nothing wrong with accepting casino sites, porn sites etc... as long as these sites are nice and clean, don't use spamy/black-hat techniques, don't link to bad neighbourhood etc. The case is that most porn sites do that, most viagra sites do that and some casino sites do that so that created a myth that you shouldn't link to eg. casino sites by default. From my experience poker sites are usually very solid SEO-wise and there is no reason to avoid them.