- Does the latter (created by myself) mean the same thing as the former?
- Is it even grammatically correct?
- Does it have a nuance to it (e.g. emphasis on it being a concert?)?
Both of your examples are grammatically correct and describe the same event. But there is a slight difference/nuance in your examples as is shown below:
このホールで時々{ときどき}コンサートがある。
このホールでコンサートが時々ある。
In Japanese, word order doesn't have as much impact on the meaning of a sentence that describes an event as in English, but it shows the focus within a sentence. When a frequency word like 時々{ときどき} is close to the verb ある such as in #2, the time/frequency of the event is focused more.
時々、このホールでコンサートがある。
コンサートがこのホールで時々ある。
コンサートが時々このホールである。
コンサートがこのホールで時々ある。
このホールでコンサートがある、時々。
コンサートがこのホールである、時々。
時々{ときどき} and other time/frequency expressions are more focused when there is a pause after it at the beginning of the sentence such as in #3, or when the adverb is placed right before the verb such as in #2 and 6, or when it is placed at the end of a sentence such as in #7 and 8.
Verbs (predicates) are the foundation of a sentence, filling in the details (5W1H: who, what, when, where, why, how) with other words. Subject nouns, which are normally marked by が in Japanese, play the 2nd most important role in a sentence; therefore, the subjects are normally focused in a declarative sentence such as #4 and 5.
このホールで in #1 is focused, because it is placed at the head of the sentence where the subject コンサートが is expected to be placed.