It's possible, but it can be avoided if theymos decide to pick people who want to volunteer instead. There's some people who actively combat spam and theymos could recruit them.
I think volunteerism is not enough to be appointed as a moderator. Some people only shows an act of volunteerism in order to gain reputation and later behaves like a scumbag. There should have a screening tool maybe when appointing a moderator just like becoming of a merit source.
Totally understandable, but obviously theymos/moderator review/research those who want to volunteer.
If theymos can't or don't want to recruit new moderator, then theymos should do something else such as disabling signature on boards with lots of spammer to punish spammer.
Such drastic measure like this shouldn't be a first option, but doing this would just push those spammers to other boards where signatures are shown. It doesn't solve the problem but just sweeps the rubbish into a different part of the house.
I only suggest this since there's no indication theymos will solve the problem in better way (or perhaps theymos suddenly introduce/do something again). I partially agree since few/some spammer with low effort will give up and reduce the problem.