My understanding is that technically a smart contract could be built using Ethereum blockchain... no need for native tokens, right?
This is correct, you can build a smart contract of any kind, tokens are not a must.
Tokens are needed not for building the DApp’s features but as an incentive for miners to use the platform, right?
This is incorrect. Miners have nothing to do with tokens. Miners are incentivised through transaction fees. Transaction fees are determined by gas, which is a measure of how much work is performed in a transaction. For smart contracts, this is directly proportional to the amount of code executed during a transaction, and the actions performed in that code. Actions such as storing data into the blockchain cost more, while simpler actions such as adding two numbers cost less.
The final fee is the
amount of gas consumed * gasPrice, which gives you an amount in ether. This amount is deducted from the balance of the address that started the transaction, and is paid out to the miner instead.
If so, then would it be possible to build a Dapp without native token and still provide a good incentive for miners to use your DApp???
Miners don't care about your dApp specifically. They will pick transactions with the highest gasPrice, and highest gasLimit to gasConsumed ratio. Your dApp should be incentivizing users to make transactions.