I have been through the background check for security purposes, i had a civillian job for the military and have a civillian CAC card. Its pretty thourough but i did not change any of my online activities.
While poling has a stigma, its not illegal, and neither is stripping or dancing for that matter. I dont see it stopping you from joining or being questioned morally. I do think its possible that the stigma could work against you advancing.
I would talk to the recruiter and sorta feel your way around it, maybe not ask about poling specifically but maybe in a general way. Personally I would follow the dont ask dont tell rule. If they never ask, i wouldnt tell. If its on the net, its there forever so even if you delete it now, they could find it if they wanted to.
I would just be careful who you talk to about it and who you let on your facebook. I hate to be so cynical, but i have seen careers destroyed over simple things just because someone could. As the saying goes, keep your head down and your nose clean, and it will all be fine. Do your job, dont cause issues, and dont give anyone a reason to mess with you and you can go far.
I am lucky in that my husband is smart and is good at his job, he has never had an issue with the higher ups, and i try and keep our personal business away from the command. I have done fitness competitions in the past and have yet to have any issues from it (and i have competed in bikini, which has a stigma itself). The poling is new but again, i keep my own stuff out of the command and dont make issues for them. Everyone knows i am very much into fitness, i dount that any of them know about the poling.