In the event of a lawsuit against a previous employer for non payment. And the evidence against them includes notarized statements from previous employees with statements towards the owner refusal to pay them. If you took them to court, and they were found guilty. Can you be sued for libel, if you put out advertisements that portray the owner/company in a negative view even though you weren't lying?
In general, one defense against libel is to prove that your statements are true.
If your employer sues you for libel, and you do not dispute that you ran the ads, you would need to prove that your claims are true. You may personally be sure that your claims are not in fact libelous (because you know they are true), but the relevant concern here is whether you can prove that your claims are not libelous in a court of law.
If your employer sues you for libel, you have the advantage that your have already organized a substantial defense. You could use the same evidence from your nonpayment case as you do in the libel case against you, which makes it substantially easier to handle the libel suit. If it held up in court during the nonpayment case, it may do well in the libel suit as well. Of course, if you do not win your nonpayment suit, then that does not speak well about the ability of your evidence to hold up in court.
Even if you do win, however, take care that the scope of your claims does not exceed what you can actually prove: if you have 10 verifiable witness statements from people defrauded by your manager, but you claim in your ad that he defrauded hundreds of people, then obviously your available evidence does not go very far in defending against the libel charge. Those ten witnesses may be enough for you to win your nonpayment case, but not necessarily enough to defend you against libel, depending on your exact statements.
As another answer already notes, stealing is quite different from nonpayment: the former implies bad-faith intent to permanently deprive you of something, while nonpayment could simply be the result of a poorly run business or unexpected financial setback. If you only have evidence of a history of nonpayment with no evidence about motivation, an accusation of stealing might be difficult to prove.
My guess as a non-lawyer is that a safe statement to make might be, "I have successfully sued Comapny X [or whoever the defendant was] for nonpayment, and included as evidence 10 other accounts of people who suffered a similar fate." Such a statement is an easily verifiable matter of public record.
Be careful what you say. Even if it is true that the company did not pay its debts, that proves nothing about the owner and vice versa. Legally they are different people and making the claim about the owner for what the company did is the same as making a claim about me for what my brother did.
Further, not paying debts isn't stealing. Stealing is taking personal property from someone with the intention of permanently depriving them of it. It's possible that a fraud was perpetrated if at the time you were engaged they had no intention of paying you, although this is clearly difficult to prove. If they haven't paid because your work was allegedly defective or they simply don't have the cash, there is no criminality at all.