Would a reduced block generation time make the Finney attack more difficult?
Assuming all else is equal (same network hashrate, etc) then the attacker still represents the same percentage of the overall hashrate and therefore may claim the same percent of the blocks for his/her attack. While it's true that faster block time increases the total number of blocks, reduces the difficulty and makes it so that the attacker has more opportunities to land an attack with the same hashrate it also lowers the detection time for such an attack and narrows the window.

In the standard Bitcoin network, a block is found roughly every 10 minutes, but realistically they are found along normal distributions with their peaks at 10 minute intervals. A block may be found immediately after another block or it may take 20 minutes to find the next block, but these are not typical cases. I don't have data to show what one standard deviation from the 10 minute mark would be, but I can say that if block time were reduced such that the region of +/- 1 standard deviation overlapped slightly, an attacker would face a statistically significant risk of a block being found before he or she could execute the Finney attack. I have no idea what other effects this might have on the network, and it would require significant testing to confirm its feasibility.

Even if the +/- 1 SD region did not overlap, the distance between their boundaries is effectively the period of time an attacker has to execute an attack, so anything which narrows this gap reduces the effectiveness of a Finney attack.

The active question which I've still not found an answer to, is this: Does the value of σ² for the distribution of block finds change along with average block time or is it somewhat static? If σ² remains the same then decreasing the block time will drastically effect the ability of an attacker to utilize this method, but if it decreases proportionally to block time then the only effect block time has on such an attack is the added requirement of greater precision in timing.

Edit: I've received confirmation that block generation isn't a normal distribution but rather a Poisson distribution and that the time window for a Finney attack does scale linearly with block time. To this end, reduced block time provides no statistical advantages over normal block time, but it does still require an increase in precision on the part of the attacker. As I've not heard of anyone executing a Finney attack, even as a proof-of-concept it's questionable how much the precision requirement would help in preventing attacks, though the effectiveness of such is probably more dependent on the merchant/business model than on the network itself.