Yes.

I'm sure Rozanne wishes that my sunlight weren't so intense but she grows and blooms in my full sun anyway. It's the only geranium that I've ever had much luck with here.

They grow fine in full sun in zone 7a in NC.

You have already had more luck with Splish Splash than I have. I grew mine from seed, I think it definitely needs a bit of shade. One plant in full sun died. I have one now that gets some afternoon shade, I think it would like more. I don't think Splish Splash is a vigorous bloomer, mine has never bloomed a lot, but perhaps it would like more shade. I have Biokova & Biokova Karmina. Biokova does better with some shade & can handle quite a bit of shade & bloom well when weather is cool. Biokova Karmina grows well in sun or shade, but does seem to rebloom better if it doesn't have the heavy mid day sun.

I have a tough time with this plant. I'm not really sure what it wants for good culture. It languished in full sun.

I have "Splish Splash" and probably "Johnson's Blue" and agree that neither is particularly vigorous. I've had the best luck with them in areas that receives a bit of relief from hot sun. I love the flowers, but I'm not overwhelmed by it, by a long shot. I won't be adding more of them any time soon.

I'll add this to the list of plants that frustrate me:
Shasta daiseys
Physostegia (I actually killed it)
Platycodon

Go figure!

With some 300 species originating from all over the globe and countless more hybrids, it's pretty hard to make a generalized statement that all hardy geraniums like the same growing conditions. Some are very happy in and prefer sun and very dry conditions, others prefer more shade and evenly moist soils. If you look hard enough, you can find a geranium to suit pretty much any growing condition, with the possible exception of very boggy soils.

FWIW, with the exception of a few notable shade loving cultivars, most will thrive in full sun to part shade in rich, well-draining yet moisture retentive soils. The alpine forms are particularly well-suited to open, full sun positions, as are renardii, cinereum, sanguineum and hybrids of x riversleaianum. Because 'Rozanne's parentage is derived from two Himalayan species, she may be happiest and perform the best receiving part shade or at least the opportunity of a cool root run.

Rozanne geranium really works best as a weaver around good sized perennials, grasses, and shrubs. The first year she may stay in a clump, as she did for me, but after that she puts out long stems and likes to climb up, over, & between other things in your garden. She can be cut back hard to keep her in bounds (sacrificing a few weeks of blooms) if you prefer, but it is easier to let them do their thing. I have 9 in my south facing mixed shrub border. As a result they get some shade from the other plants, but no overhead tree or building shade and they seem to love these conditions. For me they start blooming after a lot of my other geraniums, but continue blooming until hard frost. My garden is heavy clay and wettish but tends to be somewhat drier around my big shrubs and grasses where six of the Rozanne are planted. The other three are doing just fine in a much wetter area, but these divisions have never gone through winter there yet so I'm not sure if they will overwinter in a wet area.

Biokovo is planted in an open spot in a sunny daylily bed, the small grayleaf geraniums (cinereum Splendens) are planted along the edge of the drier patio bed, shaded somewhat by some of the other plants, and the various sanguineums, along with some Rebecca Moss (oxanianum) and Wargrave Pink (endressii) are in pretty much full sun in an island bed centered by some tall phlox and offset by a small Hinoke Cypress. The island bed started off as a holding area for sunlovers - but you know how that goes...:~)...anyway the geraniums, all at least 3 years old now & never replanted elsewhere, don't seem to mind the sun (at least in zone 5).

I have had Splish Splash and got rid of it because it wasn't a vigorous bloomer, and the blooms needed a magnifying glass to look like they do in the catalogs.

I have Bevan's Variety, and although I love it, it's a bit feisty as to where it does best. Too much shade, and it hardly blooms; too much sun (esp afternoon) and the foliage just wilts, as well as burning in the late summer. It's best with full morning sun.

I haven't grown splish splash, but I grow all my hardy geraniums in full sun. Having said that, I believe the purple leaf varieties would benefit from a bit of afternoon shade, but they do tolerate full sun.
Robin