I have heard a little bird tell me that you will also be able to monitor CAT9800 in the Meraki dashboard down the road.
But I think its somewhat far down the road, since we have just had release for monitoring of the CAT switches (and the management of those switches in dashboard is still not publically available).
So Im guessing that you are looking at a 6 - 12 months timeframe <- Pure guessing from my side.
But in theory yes, then you could monitor your 9800 both in DNA-C and The Meraki Dashboard, like you would be able to do with all your switches. - The only question is why would you want to monitor them (it) in both places ?