Can I use any DIY hubs with Lutron Caseta?
The Lutron Caséta Wireless product line isn't the best line for your needs. Yes, you will need a Lutron Smart Bridge or a Lutron Smart Bridge Pro to communicate with your Caséta Wireless devices. It is made to be end user friendly (idiot proof) to the point of not being DIY automation friendly.

Lutron hasn't published their API software publicly, but there is a PDF of their intergration protocol available. This PDF outlines Lutron's five product families that are their professional residential/commercial solutions (QS Standalone / Quantum / RadioRA 2 / HomeWorks QS / myRoom plus), and explains how to connect and send automation commands over ethernet (TCP/IP) or serial (RS-232) to each of them. Unfortunately, you'll still need to purchase a proprietary Lutron Integration Access Point for whichever product line you choose. The Integration Access Point is necessary to transmit the TCP/IP or RS-232 communications from your computer to the wireline or RF frequency the Lutron device can communicate on, but it's not as bad as adding another proprietary smart hub that tries to run everything in your house for you.

If you absolutely don't want to add another proprietary hub or don't want to limit yourself to a specific brand, then it might be better to go with a brand/protocol that easily communicates with your computer and isn't brand specific. A product that uses Z-Wave, X10, or Zigbee might be better for you, and should be supported longer than any of Lutron's lines.