Yes!
PurpleAds is totally separate from Google Ad Manager / DoubleClick For Publishers (dfp) and does not conflict with it.
You do not need to replace any existing ads/network/provider you currently have.
You can either:
Serve PurpleAds ads directly on the page in addition to GAM / DFP
Serve PurpleAds banner ad code inside as a creative in GAM
Create an Order and call it "PurpleAds Order"
Next, create a line item in the PurpleAds Order, pick "Display Ads"
For the name write "PurpleAds Line Item".
For priority start with a priority of House or Network with a $0.1 CPM.
Add all relevant iAB sizes:
120x600, 160x600, 300x600
300x250, 320x50, 320x100, 300x100, 200x200, 250x250
320x480, 336x280, 468x60
970x250, 970x90, 728x90
Finally, create a "Custom Code" creative for each size and paste the PurpleAds Banner Code, make sure to untick Serve Into Safe Frame
That's it, you're ready to go.