Both sides had lists of witnesses. The only witnesses who were allowed to testify who were on the R's list were 3 names which were also on the Dems' list. In other words, they were going to be called anyway. The other requested witnesses on the Reps' list were not allowed. So, the answer is "no" the Republicans were not allowed to called any of their own witnesses. Meanwhile, the Dems got their 17 witnesses.
On this topic generally, I want to shoot down this idea we keep hearing and seeing that trials must have witnesses. This is not true. In fact in the US, the majority of trials in federal and state courts combined have no live witnesses. At the federal level, if we include the bankruptcy courts, I would be willing to bet somewhere close to 3/4s of all trials in the federal courts have no live witnesses. Maybe more.
I just get tired of this argument getting tossed around by people who do not know what they are talking about. And, on top of all that, what's been happening here isn't even a real trial anyway. If it were, this matter would have been dismissed at the motion phase, which is to say before any discovery at all (at least in the federal courts). Which means before any depositions or collection of any other evidence.