From what I have been reading, Speech Acts are meant to be more general than Dialogue Acts. However, you are correct, there is much overlap between the Speech Acts and the difference is not apparent.
From Wikipedia's stub on Dialogue Acts:
A dialog act is a specialized speech act. For example, Question is a speech act, but Question_on_hotel is a dialog act. Dialog acts are different in different dialog systems.
Of course they only site one work there, that being Andreas
Stolcke et.al 2000 "Dialogue act modeling for automatic tagging and recognition of conversational speech".
There are other Tag Sets out there including DAMSL, SWBD-DAMSL (which is referenced in above paper), ICSI-MR, MALTUS, and a listening-oriented Dialogue Act tag set by Meguro et.al 2010. There are more too. I have found them to range in the number of tags from 6 -- 200+ (Shriberg's being the smallest and original DAMSL being the largest). The tags obviously vary and a specific dialogue tag set for open-domain does not seem to be well defined at the time being in academic literature. I suspect that the open-domain dialogue tag set will closely relate to that of Speech Acts.
Now this is only my personal view and has no grounding that I know of in academia, but it appears that Dialogue acts are really just speech acts intended for Dialogue Agents. These can therefore be either as general as normal speech acts if the dialogue agent is intended for open-domain, or more specific if there is a specific domain focused on. That is only my opinion though given what I have seen so far. That Wikipedia stub seems to back me up on this, but even then that is not the most credible source given it being a stub.
Stolcke, Andreas, et al. "Dialogue act modeling for automatic tagging and recognition of conversational speech." Computational linguistics 26.3 (2000): 339-373.
Shriberg, Elizabeth, et al. "Can prosody aid the automatic classification of dialog acts in conversational speech?." Language and speech 41.3-4 (1998): 443-492.
Popescu-Belis, Andrei. "Abstracting a Dialogue Act Tagset for Meeting Processing." (2004): 1415-1418.
Meguro, Toyomi, et al. "Controlling listening-oriented dialogue using partially observable Markov decision processes." Proceedings of the 23rd international conference on computational linguistics. Association for Computational Linguistics, 2010.