although present participles of verbs can often achieve an adjectival status, which can indeed override the true verbal form in prevalance, this is not so for oriens. both the adjectival and nominal forms are well attested throughout Latin, never would a form of esse be appended to oriens to render a progressive such as 'is rising'.
in the following
Canis infesto sequitur uestigia cursu praecipitantem agitans oriens Cic.Arat.368
cum consul oriens de nocte silentio diceret dictatorem Liv.8.23.15
riuus Herculaneus oriens eadem uia ad militarium tricesimum octauum Fron.aq.15
[sol] purus oriens atque non feruens serenum diem nuntiat Plin.nat.18.342
ne fulgor suus orientium iuuenum obstaret initiis Vell.2.99.2,
to quote but a few instances, oriens is functioning in its natural and purely verbal state.
to render present progressive as esse + verbal participle would be dog latin indeed. sum potens and such like cannot be viewed as counter examples, since potens is one of the fully lexicalised adjectival forms from a participial origin.
both Greek and Latin had severe difficulties in distinguishing the achronic present (e.g. men die) from the present general (e.g. I read books) and the present progressive. apparent counterexamples of the dictum that present progressiveness cannot be represented with esse+ptcpl., such as the early
minimeque male cogitantes sunt, qui in agricultura occupati sunt (Cat.agr.praef.)
do not demand a progressive rendering but rather merely one in adjectival terms.
the same, mutatis mutandis, applies to Greek, although there are a few strong examples where it is difficult to posit a good adjectival rendering. for instance [face=SPIonic]h(gei= diafqeirome/nouj tina_j ei]nai [/face](Pl.rep.492a) is clearly expressing a progressive sense of 'being destroyed'. i would suggest, however, that in this instance the introduction of indirect statement engenders the periphrasis, where the presence of a mere passive infinitive would not have expressed the progressiveness as lucidly.