Yes. I'm not sure what a donation is for, if not for the recipient to spend as they see fit. And this isn't a matter of spending donor money on unrelated but deserving causes - as you say, supporting clients supports the ecosystem.
I understand the argument that deciding who gets the money and how much is nontrivial and perhaps better left up to individual donors, but I disagree that it would be dishonest or misappropriating funds if you were to do so.
IMHO, most people donating to a software project would assume the funds are used for something related to that software project. Of course you can invent a narrative saying that the funds are now given to <developer> of the project, and now that he owns the money, he wants to donate to <some other project> -- it's probably a valid legal argument in case disputes arise, but it probably isn't what the original donors had in mind...
This is only my opinion, but when I donate for a software, I do it as an appreciation for the effort and time put into that software. I don't care what the owner does with that money.
I understand the argument that deciding who gets the money and how much is nontrivial and perhaps better left up to individual donors, but I disagree that it would be dishonest or misappropriating funds if you were to do so.