No! You cannot! Ang mga panghalip na siya at sila ay ginagamit lamang na panghalili sa ngalan ng tao. However, you can use "ito o iyon" so you say "Oo nakita ko iyon" :)

In the example you gave, “iyon” would be the appropriate pronoun, but using “siya” would not really be unpardonably wrong. Actually, in some situations, “siya” or “sila” may even be used instead of “ito” or “iyan” or “iyon”. Since we don’t have the exact equivalent of “it” in Tagalog, what we use instead are the demonstrative pronouns "this" or "that". However, those pronouns do still retain their sense of reference to a location – here or there. The “tore” in your example, being an immovable object, would retain its location (sa kagubatan) so referring to it as “iyon” would just be right because it would mean “that over yonder” to both A and B. When the object being referred to though is not in a fixed or permanent position or is intangible, we might use “siya” or “sila” instead.

Just thought I'd add. Often we can't and don't need to translate English exactly to Tagalog. Did you see the tower in the forest? Yes, I saw it. Nakita mo ba yung tore sa gubat? Oo, nakita ko. - a pronoun is really not necessary Did you receive/get the money? Oo, nakuha na. I got it - meaning I figured it out Nakuha rin siya=I finally got it. This is one instance I can think of where siya didn't refer to living things. Even then it's still unnecessary since "Nakuha ko rin" is enough. In my experience, (I'm a millennial by the way, so you can compare it to American youth misappropriately using an English word), we add the siya at the end to make it lighthearted. I've been toiling on this for months. Natapos ko rin siya. So, I suggest sticking with "siya" para sa mga bagay na may buhay. We don't have an exact translation for "it" because Tagalog don't really need one.

(continuation) For example, if A asks B, “Natanggap mo ba yung pera na pinadala ko sa iyo?” (Did you receive the money I sent you?), B would most likely say either, “Hindi ko pa SIYA natatanggap” or “Oo, natanggap ko na SIYA”. The reason for not using “iyon” is because the money, aside from being a movable object, is located conceptually to be in transit between A and B and not “there yonder”. If B used “iyon”, it might suggest that the money had been received and totally spent that’s why it's already “there yonder”. Another example would be, suppose A is struggling to solve a mathematical problem. When A finally figured out the correct solution, he would most likely say, “Nakuha ko na siya!” (I got it!). “Iyon” and “iyan” would definitely not be used here as they would mean “that”. “Ito” (this) is a possibility if the problem and solution are written on a piece of paper and A is showing that paper to B. In that case “ito” would be referring more to the paper or what is written on the paper he is holding. But if A is referring specifically to the solution (intangible), “siya” would be the best choice. If A was working on more than one problem, after correctly solving them all, he would have said, “Nakuha ko na SILA!”.

Grammatically it is wrong, but if you are just having a conversation, it is okay since the person can understand that you are referring to the 'tore'. Just use 'iyon' in replace of 'siya' to make it correct.