Even some Reformed who signed Dort admit it: Gomarus on Tyre's repentance (Matthew 11:21), cited by Walaeus
Even among the Reformed who subscribe to the Synod of Dort, some acknowledge in God this conditional knowledge, by which, before every decree of his will, he knows what any free cause would do in any order of things, according to its innate freedom. Francis Gomarus seems to come first among them, and Courcelles has already cited him for this view.
Commenting on Matthew 11:21, Gomarus first notes that the repentance of Tyre that would have followed Christ's miracles is to be understood as the kind common to elect and reprobate, believers and unbelievers. In his view the sackcloth repentance of the Ninevites was of this kind. He then adds these very words:
'What Christ asserts about this repentance of Tyre that would have followed under that condition is true by virtue of the unbounded foreknowledge of his divine nature. By it he knows what would have followed given an antecedent, even if neither came about. Given that condition, everyone knows that one or the other would have happened, that they would either repent or not, from the principle that two opposites cannot both be true at once. But which of them would have happened, since the matter was contingent, only he foresaw who sees all things by his infinite knowledge and foretells with certainty not only necessary things but future contingents too. A similar passage is Ezekiel 3:6-7.'
So Balduinus Walaeus reports in his commentary on the historical books of the New Testament, at the passage of Matthew cited.
Latin
XXV. Sed & inter Reformatos qui Dordracenae Synodo subscribunt, reperiuntur nonnulli agnoscentes in Deo scientiam illam conditionatam, per quam ante omne voluntatis suae decretum, novit quid causa libera quaelibet, in quovis rerum ordine, pro ingenita sibi libertate, factura esset. Inter quos primum numerandus videtur Franciscus ille Gomarus, in hanc sententiam jam a Curcellaeo citatus. Etenim scribens in locum Matth. 11. v. 21. Postquam observavit Tyriorum Poenitentiam, posita miraculorum Christi conditione, futuram, intelligi hujusmodi, quae communis est Electis & Reprobis, credentibus & non credentibus: qualis, ex ejus mente, fuit Ninivitarum cum sacco Poenitentia; subjungit haec ipsa verba, Quod autem Christus de futura hac Tyriorum, posita illa conditione, poenitentia asserit, illius veritas ex indefinita divinae ipsius naturae praescientia constat, qua novit quidnam, quo posito antecedente, fuisset secuturum, etiamsi neutrum evenerit. Nam posita ea conditione, alterutrum fuisse eventurum, ut aut poenitentiam agerent, aut non agerent, omnibus notum est ex principio illo, quod duo opposita non possunt esse simul vera: sed utrum eorum fuisset futurum, cum res fuerit contingens, solus praevidit, qui infinita sua scientia omnia videt, nec solum necessaria, sed etiam futura contingentia certo praedicit. Similis locus est Ezech. 3. v. 6, 7. Ut refert Baldvinus Walaeus commentario suo in libros historicos Novi Testamenti ad locum Matthaei citatum.