Can an Ultegra or 105 short cage RD handle a 30T ?
As I said in a comment, there are 25+ years of 105 and Ultegra (well, ultegra was called something else back then, but the line has been around for quite a while), so you need to find the right 105/Ultegra you're talking about.
You can find the Product Info at this link.
In 11 speed: The Ultegra RD-6800-SS and 105 RD-5800 SS both have a 28t max. Thus, Shimano doesn't recommend you run a 30t with a short cage. The RD-6800-GS and RD-5800-GS both have a max of 32t.
In 10 speed: The 105 RD-5701-SS has a 30t max.
Note that Shimano has mucked up cable pulls between 10 and 11 speed road, so you can't just put a 10 speed RD in a 11 speed system.
Note that also there may be several RD's under the same group under the same year or # of speeds (e.g. in the Sora case), so you need to look up the particular RD you want to use.
It's worth mentioning that most max tooth specs are on the conservative side. Meaning that if you put your drive train into inappropriate combinations you would expect problems if you used a cog bigger than recommended. If you already know not to use the gear combos of "little cog in the front, little cog in the back," and, "big cog in the front, big cog in the back," then you could squeeze a bigger rear cog. Of course this is not recommended, but it's fun to know and play around with.