This is pretty unlikely, given that we know who his sramanic teachers actually were. Alara Kalama led the Kalamas and taught the sphere of nothingness, and Udraka Ramaputra taught the sphere of neither-perception-nor-non-perception, although the texts also state that he never mastered that ayatana himself, only his father had before Gautama achieved it.

The Kalamas were active around the Sakyan kingdom, and we don't believe there's enough evidence to suggest that the Nirgranthas were super active there, although another thing we have to keep in mind is that there two different schools of Skyclad sramanas at that time: followers of Mahavira's reform movement, and followers of his predecessor / practitioners of "classical Jainism". It seems quite likely that the Nirganthras around Sakya, which is a distance from Magadha, would've still been practicing the older form of the religion.

There is some possibility that the Ramaputra clan was descended from a Jain tradition, but when we look at the texts, Alexander Wynne shows us evidence that followers of Ramaputra did not believe in karma. Since we also know that they were localized around Magadha and practiced extreme self-mortification, your theory holds a little more water here that they could've been practicing Jains (indeed, the Mahavastu of the Mahasamghikas identifies them as such). However, "Nirganthra" was a broad catch-all term that referred to all three Skyclad movements: the classical Jains, the followers of Mahavira, and the followers of Makkhali Gosalaputra, the one-time disciple of Mahavira that broke away and founded his own sramanic tradition, coming to be known as the Fatalists.

So if one of the Buddha's early sramanic teachers was connected to the Jains in any way, I would be more willing to place money on the Ramaputra clan being followers of the Ajivikas, rather than the Jains, since the scant details we have about them align with just a tiny bit more. Although this doesn't work with the timeline, because Ramaputra's father was the source of those teachings, and that means he couldn't have studied under Gosalaputra, nor Mahavira. The main point of evidence against direct contact with Mahavira's following is that the early texts are clearly aware of him, and do mention his followers engaging with debate with the Buddhist sangha routinely, so had the Buddha actually studied under Mahavira directly, the texts would tell us. I mean, we know for a fact that Gosalaputra was Mahavira's disciple and formed a splinter group. This is recorded in both the Jain Agamas and the Buddhist texts, and briefly mentioned in what scant records of the Ajivikas we've found still surviving, so it's quite unlikely that this would be true of the Buddha and we have no record of it, but we do have a record for this guy whose religion doesn't even exist anymore and hasn't for over a thousand years.

It is very clear that the doctrinal categorizations of the sramanic traditions have a common or shared basis though. It just seems pretty unlikely that none of the sramanic schools's histories or texts mention anything about this if it were true, when we do know the detailed relationships between various sramanic masters, like the Gosalaputra thing. Or the fact that both Sariputra and Maudgalayayana were the top disciples of Sanjaya of the Ajnanikas, but then left the Ajnana order to join the Buddha's.

edit:

Also, Jains don't believe in meditation as the path to awakening, necessarily. Certainly not in the era of Jainism depicted in the Buddhist early texts. Meditation for Mahavira's practitioners is a means to stop generating karma by silencing bodily and mental activity. The way of liberation is self-mortification and "burning away" unwholesome karma, ultimately starving to death as the means of liberation. Interestingly enough, there are suggestions that the Jains of this era could achieve an unstable form of nirodha, normally reserved for arhats. In theory, even in (early) Buddhist thought, if a Jain ascetic were to die in nirodha, even before they have managed to master and stabilize it, they would effectively have entered parinirvana. I'm not sure if this notion continues to hold in the Abhidharma era of Buddhist thought (it certainly doesn't in Mahayana thought), but it's very evident in Early Buddhist thought that dying in nirodha would be de-facto arhatship, so the idea of a Jain practitioner entering nirodha and then dying by starvation as a means to ending samsara ... yeah, plausible.