He wrote that the Church authorities have said that one may use the covid vaccines if there are very serious reasons, but then he included that sentence from dignitatis humanae that talks about not being forced to against your conscience, as an ad hominum argument. He doesn't agree with taking the vaccine at all, but he included that paragraph because your employer will most probably bring up how the Pope approves of the vaccine.
Forgive my skepticism, but why is he endorsing an exemption letter which contains teachings he allegedly opposes?
According to your interpretation, his letter is arguing with itself, first articulating what he admits/alleges is Catholic teaching about allowing abortion-tainted vaccines in certain circuмstances (appoint you are in denial on), then quoting DH to say, apparently, those Catholics who object to what he just called Catholic teaching (?!?), their unCatholic, erroneous consciences must be respected.
I suspect that if I corner him, and ask whether it is ever permissible to take abortive vaccines, he will say yes.
if his position is no, he needs to chop out the portion of his letter which contradicts him.
As it stands, that letter has little value for the accomplishment of its stated purpose.