In alot of cases yes, pulls the oil out and onto the MAF sensor causing codes to set. I think they are ok if you do not over oil them but with out enough oil they do not filter well! Lots of guys run oil filters with no issues but they have caused lots of problems for others. Its all in what you want i would say but you really cant find a intake setup that dosent use a oiled filter!
They really add little to no hp, I made 460 hp with stock intake with just a bunch of holes drilled in the bottom half of the air box!
Hope this helps,
Caleb