Security of cloud computational protocols in UC Framework?
I think it is still possible to use UC in this case.

Recall the setup for the UC framework. We have an ideal world and a real world. There are parties $P_1,\dots,P_n$ in each world and an environment $\mathcal{Z}$ in each. In the real world we have the adversary $\mathcal{A}$ while in the ideal world, we have an ideal functionality $\mathcal{F}$ and a simulator $\mathcal{S}$. In the real world, the parties run some protocol $\pi$ while $\mathcal{F}$ should compute the same functionality as $\pi$ in the ideal world and be secure by definition (basically it is a trusted 3rd party). See the graphic below (taken from Martin Geisler's PhD thesis)



So, in your case, you have 3 parties. $P_1=\text{Alice},P_2=\text{Bob},P_3=\text{Sally}$. I'm not going to mess with specifying the protocol $\pi$. In the ideal world we can have a very simple setup. $P_1$ and $P_2$ submit their inputs (in plaintext over a private channel) to $\mathcal{F}$ and $P_3$ issues commands to $\mathcal{F}$ with what to do with those inputs (e.g., "compute the sum", etc).

In the real world $\mathcal{A}$ is basically $P_3$, so we assume that anything $P_3$ knows, $\mathcal{A}$ also knows. That information is then leaked to $\mathcal{Z}$. Then in the ideal world, you'll have to construct $\mathcal{S}$ in such a way that $\mathcal{Z}$ cannot distinguish between the two worlds. How exactly you do this will depend greatly on $\pi$.

As an example, let's say we are just computing the sum of the inputs using Paillier. In $\pi$, $P_1$ and $P_2$ might encrypt their inputs with the Paillier public key (who knows the private key is up to you, but it shouldn't be $P_3$) and send them to $P_3$. Then, if $P_3$ decides to, it will homomorphically sum the values and send the resulting ciphertext back to $P_1$ and $P_2$. To make it general, we'll just let $\mathcal{Z}$ provide $P_1$ and $P_2$ with their inputs and with $P_3$'s choice.

In the ideal world, $P_1$ and $P_2$ pass their inputs (from $\mathcal{Z}$) to $\mathcal{F}$. Then, if $P_3$ tells $\mathcal{F}$ to compute the sum, $\mathcal{F}$ does so. Furthermore, it will leak an encryption (using the paillier public key) of the result to $\mathcal{S}$ who passes that to $\mathcal{Z}$. You can also have $\mathcal{S}$ leak encryptions of the inputs to $\mathcal{Z}$ in a similar manner.

In both worlds, $\mathcal{Z}$ sees encrypted inputs and an encrypted output (if $P_3$ decides to allow the computation). Thus the two worlds are indistinguishable (assuming IND-CPA of the cipher) and the real world is as secure as the ideal world.