In general absolutes and crystaline fragrance compounds will dissolve better and in a higher percentage when you heat up the mixture (of course with extreme caution because alcohol is very flamable). The drawback is that it only works as long as the temperature is elevated, at the moment you cool it down it may (partly) get solid again. Heating may speed up the proces, but it will not make any substance better soluble. Speeding up is of course good, otherwise it may take weeks before the substance is dissolved completely.
For a single substance like coumarin you can look up the literature for solubility, but even then it doesn't always work as you would expect. For instance according to the literature is 20 gram coumarin soluble in 100 gram 90% alcohol at 20 °C. When you try, you will find that it is hard to get a solution as strong as that, 10% seems to be the strongest solution for practical use. This happens partly because even a single substance like coumarin has some impurities that make it better or less soluble. These are different from batch to batch.
Vanilla absolute is not a single chemical, it is a chemical cocktail, consisting of hundreds of chemicals. Because the exact composition can be different depending on age, manufacturer, composition of the vanilla beans used (that depends of geographical origin, botanical variations ...) etc. the chemical composition will be different for each batch. Therefor it is harder to find accurate literature data on solubility, the best way here is trying, but it is possible that 25% is possible with one batch and only 5% with another.