Are there any particular connotations for worker here? Would it imply manual labor, or is it more all purpose?
Interesting that "é" is needed even when a more specific subject is named.
The “sub-subject” pronoun in a classificational copular statement with a definite subject is optional in Ulster Irish.
I said "The worker is my uncle" and got marked down. this should be accepted.
"My uncle is a worker" is a "classifactorial clause" of the Copula,(you are assigning your uncle the classification of worker) and the structure is Is + Predicate + é/í/iad + Subject
The subject of the sentence "My uncle is a worker" is "my uncle" - m'uncail, the predicate is "a worker" - oibrí, so Is oibrí é m'uncail is "My uncle is a worker".
"The worker is my uncle" is an identification clause - you are identifying the worker as your uncle, and "the worker" - an t-oibrí is the subject, and "my uncle" - m'uncail is the predicate. The structure of an Identification clause is IS + é/í/iad + P + S so
Is é m'uncail an t-oibrí is "The worker is my uncle".
can this also be used to mean my uncle is a hard worker, in addition to he is a worker (in a specific job)?
"worker" is a noun in both of those cases, so oibrí is appropriate, though I'm not sure exactly how you'd say "a hard worker". The NEID offers ag obair go crua for "working hard", but I'm not really sure that you'd use crua for "a hard worker", because it usually connotes hardness/stiffness (crua-adhmad, cruabhruite.
docht and crua seem to overlap in some of this type of phrase -
Greim crua - "tight grip", Snaidhm chrua - "fast knot", Buille crua - "hard blow"
Greim docht - "tight grip", Snaidhm dhocht - "tight knot", Buille docht - "severe blow"
Ag obair go crua - "working hard", Lá crua oibre a chur isteach - "to put in a hard day’s work", Seachtain d’obair chrua - "a hard week’s work" ("a week of hard work" or " a hard week of work"?)
Obair dhocht - "tough work"
Tá géarbhach crua gaoithe ann - "it is blowing hard"
Gaoth dhocht - "stiff wind"
Looking at many of the examples for crua in the FGB, it seems that crua is used in many of the same ways that we use "hard" in English (physically stiff, difficult, cruel, etc) and that oibrí crua can be used (it is used as an example in the NEIDs definition of "industrious", though I prefer the EIDs oibrí dícheallach.
Thug siad am crua do "they made things hard for him" (they gave him a hard time)
An bheatha chrua - "hard life"
An braon crua - "strong drink" (a drop of the hard stuff)
Croí crua - "hard heart"
uisce crua - "hard water" .