In The Standard, 3rd January 1900, I found that the Terms of Service for the Imperial Yeomanry, according to the Secretary of State's instructions, included -
"If discharged in consequence of wounds, injuries, or disability received or contracted while on service, he will be entitled to pension in accordance with the Royal Warrant for Pat, etc., of the Regular Army." On completion he'd get a gratuity of £5, plus any other gratuity paid to troops at the end of the war, so seemingly, there was no other pension for the IY.
However, I also found this....
"The Central News says the following information was issued from the War Office at 9 o'clock last night regarding the formation of an Imperial mounted force for service in South Africa: - "The Imperial Yeomanry were enlisted under the following conditions: - Each man to receive pay and allowances at cavalry rates - i.e., 1s 2d per day - from the date of enlistment; married men to receive separation allowances; on completing their term of service the men to receive £5 gratuity, in addition to any gratuity given to the troops at the end of the war; pensions and gratuities to be paid according to Regular Army rates."
The Western Gazette, Friday 28th December 1900
So that doesn't really help you!