As I understand it, if you have coverage through your employer, you are allowed to purchase coverage through the exchange. However, you are not eligible to receive subsidies.
If it were me, I would ensure that my employer-provided coverage had expired, before my plan purchased through the exchange took effect, just to make sure there no problems.
Contentedly ER, with 3 furry friends (now, sadly, 1).
Planning my escape to the wide open spaces in my campervan (with my remaining kitty, of course!)
On a mission to become the world's second most boring man.