Yes – at least it's very likely, but it is far from clear which. Kenneth Woodward, in his Making Saints, notes that "many cases do not succeed" – but since judgement is rendered on an overall case, comprising many documents other than the arguments of the Devil's Advocate, and since no commentary is issued on the judgements that are rendered, it is impossible to be sure whether any cases have been rejected explicitly as a result of the Advocate's work. In addition, while the prospective candidate for sainthood has already passed several other tests by the point his case reaches the pope for final approval, and while the Advocate's material is the only explicitly negative portion of the documentation that remains, the decision is the pontiff's – and a reigning pope is perfectly entitled to take account of some other, unstated, factor not contained in the process documents in rendering a judgement.
Breaking all this down a little further, it's important to recognise two things. First, the lawyer popularly known as the Devil's Advocate was not literally some evil agent provocateur seeking to throw a spanner in the works of the church establishment; rather, he was a key bastion of orthodoxy, whose official title was actually Promoter of the Faith, and whose role was to help ensure the worthiness of candidates for sainthood. Secondly, while the procedure created by the church to assess such cases (which was in place from 1587 until its abolition under John Paul II in 1983) was adversarial – with the Devil's Advocate debating with an advocate for the candidate for sainthood – the role of the Promoter of the Faith was only one part of a much larger process. His advocacy, moreover, was never conducted in the form of an actual trial. Rather, the two advocates pitched written arguments back and forth, often over a period of decades, seeking to hone their arguments regarding the case before them.
The two advocates taking part in this stage of the canonisation process (called the Ordinary Process) were supplied with materials assembled by the local bishop, who was charged - as a first step - with collecting evidence and with determining that the candidate was not the object of a public cult. For several hundred years, the next stage in the process was for this evidence to be reviewed by censors for any evidence of unorthodox teachings or of heresy; it seems certain that far more prospective saints were disbarred as a result of these two steps than were ever failed by the work of the Devil's Advocate. One example is Jean-Jacques Olier, the 17th century French founder of the Society of Saint-Sulpice, who was proceeding slowly towards canonisation in the 19th century when a publication of his containing unorthodox views on the Virgin Mary was uncovered. Olier's process was immediately halted. Since 1940, the advocates of a candidate for sainthood also have to obtain a declaration of nihil obstat ("nothing objectionable") from Rome, which is based on a search of the files of the Congregation for the Doctrine of the Faith – the group responsible for maintaining the well-known Index Librorum Prohibitorum, or list of banned books.
The adversarial phase in which the Devil's Advocate participated began after these checks. It started with the selection of a "postulator", a lawyer who would argue the prospective saint's cause, who was selected from a group of canon lawyers (still in existence and currently around 200 strong) recognised by the Congregation. The postulator, in turn, selected his own Devil's Advocate from among a smaller group of around two dozen lawyers licensed by the Holy See to handle such cases. Both men received copies of the materials produced by the local bishop, examined them, and began to engage in a dialectic, which might, as noted above, go on for decades, but which eventually produced a printed positio which incorporated the materials produced by the bishop and the key arguments of both advocates.
It was this positio that was considered by the cardinals and prelates associated with the canonisation process, and which went to the pope for approval. But this was not (and is not) the end of the process. Cases that passed this initial test went into a new "Apostolic Process" in which the office of the Promoter of the Faith drew up a new set of queries relating to the virtues of the candidate, which had to be considered by a new tribunal held in the candidate's diocese. This collected additional evidence - from eyewitnesses where possible - which was sent back to Rome and used in the preparation of a new document, the informatio, which systematically laid out the case.
The Devil's Advocate and the advocate for the putative saint would again register points for and against the candidate, based this time on examination of the informatio, which would again be printed, and would again be studied by the Congregation; and this entire process was repeated three times, with the advocates on either side getting repeated opportunities to advance new arguments and respond to existing ones. The pope himself would take part in the third of these exchanges, and only candidates who received the final approval of the pontiff could proceed.
But even that was not the end of the procedure - those candidates who survived examination of their credentials still had to go through the processes of beatification and then canonisation, meaning that between two and four miracles had to be attributed to them and accepted as genuine as a result of separate studies by the Consulta Medica, a tribunal of Catholic doctors tasked with assessing evidence assembled to show that a reported cure could not be anything but miraculous. In addition, beatification was subject to a final sign off which might be, and sometimes was, put on hold if the candidature was politically sensitive (for example, in the case of a martyr who had died at the hands of a regime that was still in power by the time he or she came up for consideration). Typically there has always been a further delay between beatification and canonisation, during which more miracles are required to occur. Since the late 19th century, the act of canonisation itself has been made by infallible decree of the pontiff, meaning that it is not something that can ever be reconsidered or withdrawn.
Finally, it seems incontestable that the pontiff takes a key role not only in the process of canonisation, but also in the selection and acceptance of candidates, and can steamroll the entire process if he wishes – as John Paul II did in 2002 in the case of Juan Diego Cuauhlatoatzin, the main actor in the supposed visions of the Virgin Mary that took place at Guadalupe in Mexico in the early 16th century. There is considerable doubt as to whether Juan Diego actually existed at all, so his canonisation is good evidence that the elaborate process set out above is, at least in certain circumstances, more window-dressing than serious investigation in any case. So is the dramatic increase in the number of beatifications and canonisations dealt with by John Paul II, who not only abolished the devil's advocate's role but also, in the course of his 27-year reign, approved the candidacies of more people than all other popes put together since the modern system was created in the 17th century. So, arguably, is the controversial canonisation of Josemaría Escrivá, founder of Opus Dei, which was at least in part the product of the investment of significant resources in creating and arguing his case by the members of his own order.
Still, all in all, the process of canonisation has been, more often than not, a very protracted one (Benedict XIV, in the 18th century, set the timescale as a minimum of 100 years, a ruling that is no longer in effect; John Paul II was canonised in 2014, only nine years after his death). It's one in which the Devil's Advocate played an important but far from central role. Candidates for sainthood might fall out of the process at any time, for a variety of reasons, and while successful objections lodged by the Promoter of the Faith are certainly one possible cause of the failure of a candidacy, such failures were never formally announced as such.
Sources
John L. Allen, Jr., The Future Church: How Ten Trends are Revolutionizing the Catholic Church (2009)
John Cornwall, Hitler's Pope: the Secret History of Pius XII (2000)
___________, "A game of miracles: how saints are made," New Statesman 25 July 2013
Donald S. Prudio, Certain Sainthood: Canonization and the Origins of Papal Infallibility (2015)
Kenneth Woodward, Making Saints: How the Catholic Church Determines Who Becomes a Saint, Who Doesn't, and Why (1996)