How cotranscription events affect splicing?
Co-transcriptional splicing (CTS) is very widespread. Different studies (which are done on different cell types) report different frequencies of CTS. Most of them report a frequency of ~0.8 in different cells except for mouse liver which was reported to have a frequency of 0.45
This is the article that summarizes these different studies. 

Can transcription regulators influence splicing during cotranscription? 

Yes.. including factors such as nucleosome positions.. this post may be helpful.