Background

SLA relies on the properties of UV-curing Resin. Most currently available UV Curing Resins harden to a solid, hard polymer, but that doesn't mean there are no other UV curing resins that are elastic. Most however will not be suitable for SLA or DLP systems!

Polyurethanes, which can be flexible if cured in the right way, have not come onto the market as suitable SLA/DLP printing material and up to now, I have only found one UV hardening resin on the market - the one offered by FormLabs and identified by OP

Patent History

Indeed, elastic resins are actually quite new. The first patent I could find for an elastic resin was 2003 for an elastic epoxy resin, while subsequent elastic resins were brought to Patent are different like the 2007 elastic olefin resin. In fact, there is a 2013 US patent on SLA Resin, which is still in effect. As a result of such patents being still in effect or just out of protection times, the market is still very much limited because most manufacturers simply lack the knowledge of how to do it or the licenses to be allowed to do it. In fact, Formlabs is named on 43 patents for 3D printers and accessories, of which only 1 is expired as of July 2020. I could not identify the patent that might be in use for their flexible resin, but the marketing material is of May 2020, so it is relatively new on the market and might not have been updated into either the patent database or FormLabs did buy an exclusive license for the material from someone else, meaning they will not show up as Assignee in it. Or it is kept a trade secret.

Material implications

The printed mold will probably be of a different stiffness than a cast mold as you work with a totally different material and your new molds might degrade at a different speed than urethane or latex cast molds. To get a feel for this this, you will need to run some experiments. As FormLabs hands out test specimens of their print materials, you might order the two flexible ones and then test their stiffness and suitability for your uses by having them interact with your casting resin and seeing if they break down and if you can remove them easily.

Food grade

Generally don't consider anything that comes directly from a 3D printer certifiable food safe, as you need to have both a process and a material that is food rated. There are ways to use the resulting parts to manufacture food safe objects, but that's elaborated for example in some of the questions I suggest to look into