Certainly not via route servers or typical bilateral peering configurations - but transit-over-exchange is a thing, if you can find an exchange participant willing to offer it to you.

Yes, but the question is, is transit over exchange better/cheaper than buying a crossconnect? Worst case you've just introduced another dependency that costs money and adds complexity. If you're on an IXP, you're already somehow in a data centre anyway… that will have been the hard part in most cases…