Elena:
Previously, Elena did not retain many options off of her low attacks, despite having great normals. According to ComboFiend, the development team has addressed this issue, and in Ultra Street Fighter 4, she will be a "fun, mid-ranged character," with an up-close, high / low mix up game.
Rolento:
Rolento has been known to be equipped with ways of controlling space both offensively and defensively. His movement and style are being preserved in USF4.
Hugo:
ComboFiend notes that each of the grapplers in SF4 have a distinct style, (i.e. Zangief has combos, T. Hawk has air control, etc.) Hugo's strength will lie in his corner pressure.
Poison:
Poison's playstyle will differ from her Street Fighter X Tekken incarnation. In SFxT, she was equipped with all the tools she needed to play at any range, but did not have much damage output. According to the blog, that won't be the case this time around, as she will have tools to play up-close, but will still be able to battle projectile characters at mid-range.