How would i do polkadots in buttercream?? I want the dots to be level with the icing.

About the only thing I can think of is to thicken your b'cream w/more powdered sugar/cornstarch and pipe them on wax paper to dry a bit . Maybe even use a rolling pin *very lightly* so they are all even in thickness. You can let them dry (overnight) OR fz them. Lift off w/a spatula.
They still won't be perfectly level w/the surface b'c but will be like adding fondant ones.

I figured them out!! Just ice the cake smooth then pipe Dots onto the icing then use the viva towel method to smooth them out. I made a practice ladybug. Im doing a babyshower cake , her theme is Mod ladybug so im gonna have two round tiers polkadotted then a ladybug made out of half of a ball mold. Its going to be cute.

I guess I'm too late for ya..........just wanted to say that I don't know if you've seen the "melvira method" or not, but basically you use a high density foam paint roller to roll the icing once it has crusted over (much like you would with a viva) but it actually gets it EVEN smoother than the viva, can you imagine?? LOL it's awesome!!!
Anyhow, I did a camo cake like that.......piped on the different colors and then used the roller over them and it meshed them all together without changing the shape of them at all (although it wouldnt have really mattered with the camo, but for you with polka dots it would, so I just wanted to let you know that it DOES work)

Good luck with your cake, don't forget to post a pic!