Can a strata corporation use a caretaker suite as collateral for a mortgage?

Yes, with ¾ vote approval as long as the caretaker suite is a common asset owned by the strata corporation.
Pursuant to section 79 of the Strata Property Act, SBC 1998, c.43, a strata corporation must obtain ¾ vote approval of the owners before granting a mortgage and the documents executed by the strata corporation granting the mortgage must conform to the enabling resolution.

Note that a strata corporation is prohibited from granting a mortgage over a caretaker suite if it is designated as common property in the registered strata plan.