Well, it doesn't affect the collapse of the Lib Dem vote, which, in a lot of blue-orange marginals, meant that a Conservative vote that hadn't been enough to beat the Lib Dem vote in 2010 was large enough to beat the multiple-ways-splintered non-Conservative vote in 2015. Going by
this data, the net gain in Conservative seats came from Lib Dems rather than Labour.
What's difficult to tell is how many Britons in red-blue marginals voted Conservative because they didn't want a party that wanted to dismantle the United Kingdom anywhere near power (in spite of Ed Miliband's assurances that he wouldn't cooperate with the SNP even if it meant the difference between him being Prime Minister and not) and how many voted Conservative because they didn't trust Labour to run the economy, because they didn't want Ed Miliband in particular to be Prime Minister or because of the particular candidates they had rather than national issues. The former would change in this scenario; the latter wouldn't.
Frankly, it's sufficiently difficult to tell this that I don't believe anyone can make any detailed claims on the matter with much confidence. A hypothetical Conservative-DUP coalition at the moment would have 15 more seats than the magic number of 325, which I
think is a big enough number that, unless the loss of the SNP factor
hugely affected red-blue marginals in OTL, the Conservatives plus the DUP would still have an overall majority; but it would be a slim one and the Conservatives would have to be giving lots of extra money to Northern Ireland for fear of losing the majority whenever the DUP got pissy. It would be a bloody uncomfortable situation for the Conservatives; if at any point before a big vote the DUP said that they weren't very comfortable with it and would need more incentive to vote for the government, the Conservatives would have to give more subsidies to Northern Ireland. Also, Conservative backbenchers such as Cash, Redwood and the Europhobic merry men would have a very strong hand indeed against government policy, which would in many ways drag the government to the right.