In the end, I think you just need to be ultra clear on what you want to do with your pup. If you EVER want to do obedience or agility, might as well find a new trainer, in my opinion. Never, in either of those sports, do you pause on the contact equipment.
However, if you are certain that you never want to do one of those two dog sports, then I see no issue with teaching your dog to be obedient no matter what is under their feet.
But honestly, as someone who is training for agility, you should be amazingly certain you never want to participate in those things if you are going to teach a sit or down (how is that even possible!?) on the top of an a-frame.
RATCHX3 High Jinks vom Neuanfang - Gotchya Day: 1/23/2013 DN, SG, SR, CA
Inspire Spark to Ignition! (Ignite) Gotchya Day: 10/8/2016
C-ATCH Pimg - RATO, UJJ (x2), DJX, HIT, CA, CGC, High in Games, Reserve High in Standard- CPE Nationals 2014