TL; DR: You can use responsible as a noun, but use caution; it's not (yet) standard, and will likely not be well-received in most contexts.
Although this usage of responsibles is relatively recent, having adjectives that are also countable nouns isn't. Think of individual, elder, lovely, etc. The conversion process1 may also be more ubiquitous than we may imagine. Most of us probably distinguish recyclables from other trash, and you may also remember the recent film series The Expendables.
The conversion of an adjective to a countable noun does seem to be especially popular in a business setting. An early example is employables (and un-employables):
Under existing laws a man who can work on W. P. A. is considered to be
employable; and employables, regardless of their actual employable
status in relation to private business, are barred from relief
benefits. (Hearing of the US Senate Committee on Appropriations,
Do you think there are groups who will always be unemployable? . . .
If so, should the responsibility for un-employables rest with
individual families or should they be given public assistance? (Omar
Goslin & Helen Storen, American Democracy Today and Tomorrow,
1942. Possibly the text from a survey question.)
A very common, much more recent example is deliverables:
Deliverable is a term used in project management to describe a tangible or intangible product or service produced as a result of the
project that is intended to be delivered to a customer (either
internal or external). A deliverable could be a report, a document, a
software product, a server upgrade or any other building block of an
overall project. (Wikipedia)
Whether you are producing products for your customers or reports for
your employees, your small business will have projects and those
projects must have deliverables. (Miranda Morley, "Examples of
Project Deliverables", Houston Chronicle's Small Business Chronicle,
As a final note, I've seen many deliverables “rushed out the door”
when time is tight and customers and/or clients are watching. (Bernie
Roseke, "Make All Project Deliverables Count", Project Engineer,
This is by no means an exhaustive illustration; these are just the first two words I thought of, and the first few examples I ran across.
But why do some adjectives make the jump to countable nouns, instead of only being used as mass nouns? I suspect it has to do with the desire to connect the adjective to particular instances. That is, "the unemployable" are a seething mass of non-individuals who share the characteristic of being unemployable; "unemployables" are individuals who are defined by their unemployability (at least in whatever context they are labelled this way).
In this case, responsibles are individuals who bear special responsibility for something. It might be handier to use this catch-all phrase than to specify which entities are responsible, for example if you wish to cover both individuals and departments or individuals at varying levels of authority or with different kinds of responsibility. As mentioned in comments, those responsible might also be less apropos if it wrongly implies causation.
Keeping all that in mind, it isn't a common usage, and I think the reaction of other commenters and answerers suggests that it would not be well-received outside of certain contexts. I would consider it an example of corporate-speak, which tends to be deprecated, at least until it enters the mainstream.
1 For an older example of the progression from adjective to countable noun, the word essential is first attested in the OED as an adjective, as early as c.1340. Essentials appears as a noun, solely in the plural form, in the seventeenth century, with the singular usage arising in the nineteenth. ("essential, adj. and n." OED Online. Oxford University Press, September 2016.) Nowadays it's literally countable: The 1 Essential, The 2 Essentials, 3 Essentials, etc.